Developmental changes in membrane Ca2+ and K+ currents in fetal, neonatal, and adult rabbit ventricular myocytes.

Huynh, Tracy; Chen, Fuhua; Wetzel, Glenn T.; Friedman, William F.; Klitzner, Thomas S.

doi:10.1161/01.res.70.3.508

Cited by 114 publications

(69 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Relative to other inward rectifier K ϩ channels, K ATP channels are expressed at high density during early developmental stages and therefore may have an important physiologic role during this period (1-3). However, K ATP channel activity is strongly up-regulated during postnatal development in parallel to that of the classical "inward rectifier current" I K1 (52). Our data demonstrating up-regulation of individual K ATP channel subunits during development are consistent with this increased K ATP channel current during perinatal development.…”

supporting

confidence: 80%

Expression of ATP-Sensitive K+ Channel Subunits during Perinatal Maturation in the Mouse Heart

et al. 2005

View full text Add to dashboard Cite

Prevailing data suggest that sarcolemmal ATP-sensitive (K ATP ) channels in the adult heart consist of Kir6.2 and SUR2A subunits, but the expression of other K ATP channel subunits (including SUR1, SUR2B, and Kir6.1) is poorly defined. The situation is even less clear for the immature heart, which shows a remarkable resistance to hypoxia and metabolic stress. The hypoxia-induced action potential shortening and opening of sarcolemmal K ATP channels that occurs in adults is less prominent in the immature heart. This might be due in part to the different biophysical and pharmacological properties of K ATP channels of immature and adult K ATP channels. Because these properties are largely conferred by subunit composition, it is important to examine the relative expression levels of the various K ATP channel subunits during maturation. We therefore used RNAse protection assays, reverse transcription-PCR approaches, and Western blotting to characterize the mRNA and protein expression profiles of K ATP channel subunits in fetal, neonatal, and adult mouse heart. Our data indicate that each of the K ATP channel subunits (Kir6.1, Kir6.2, SUR1, SUR2A, and SUR2B) is expressed in the mouse heart at all of the developmental time points studied. However, the expression level of each of the subunits is low in the fetal heart and progressively increases with maturation. Each of the subunits seems to be expressed in ventricular myocytes with a subcellular expression pattern matching that found in the adult. Our data suggest that the K ATP channel composition may change during maturation, which has important implications for K ATP channel function in the developing heart. ATP-sensitive K ϩ (K ATP ) channels are robustly expressed in the immature heart (1,2). However, K ATP channels in the immature heart may differ in several respects to those of adult cardiac tissue. In immature rabbit ventricle, K ATP channel open probability is roughly the same as in the adult, but they exhibit a significantly smaller single-channel conductance (~55 pS) and channel density, as defined by the number of open channels per patch (3). In the immature rat heart, K ATP channel density is also high, but the single-channel conductance and the mean open time are the same as in the adult (2). Reports describing a smaller unitary conductance in neonatal rat atrium (4) suggested that there may be regional differences. The immature rat heart K ATP channel has a lower open probability, and the channels are much more sensitive to block by intracellular ATP (2,5). In addition to these biophysical changes, there are reports that immature K ATP channels may have a different pharmacological profile. The neonatal atrial K ATP channel shows a unique functional and pharmacological profile resembling the pancreatic ␤ cell channel for its unusually high affinity for glibenclamide and diazoxide (4,5). These characteristics suggest that neonatal K ATP channels may differ in their molecular composition relative to the mature heart. K ATP channels are believed to be hetero-...

show abstract

supporting

confidence: 80%

Expression of ATP-Sensitive K+ Channel Subunits during Perinatal Maturation in the Mouse Heart

et al. 2005

View full text Add to dashboard Cite

show abstract

“…5). Systolic [Ca 2ϩ ] i , C m , and I Ca density were larger in adult than in 3-wk-old rabbit ventricular myocytes, in agreement with previous reports (37)(38)(39). In an earlier study (2), we found larger and faster sarcomere shortening in the adult myocyte, consistent with its higher systolic [Ca 2ϩ ] i .…”

Section: Discussionsupporting

confidence: 92%

Development and Cardiac Contractility: Cardiac Troponin T Isoforms and Cytosolic Calcium in Rabbit

et al. 2006

View full text Add to dashboard Cite

Cardiac contractility depends on calcium sensitivity of the myofilaments and cytosolic free calcium concentration ([Ca 2ϩ ] i ) during activation. During development, the cardiac troponin T isoform cTnT 1 is replaced by shorter cTnT isoforms, including cTnT 4 , and changes occur in other myofibrillar proteins and in calcium regulation. We expressed rabbit recombinant (r)cTnT 1 and rcTnT 4 in Spodoptera frugiperda cells and determined their effect on calcium binding to TnC in solution and on the calcium sensitivity of myofilaments in skinned rabbit ventricular fibers in vitro. We measured [Ca 2ϩ ] i and L-type calcium current (I Ca ) in ventricular myocytes from 3-wk-old and adult rabbits. Adult myocardium develops more force than fetal myocardium (1). Adult cardiac myocytes shorten further and faster than immature myocytes (2). Potential contributors to these differences include developmental increases in calcium ([Ca 2ϩ ] i ) transients and calcium sensitivity of myofilaments (1,3). Calcium transients increase postnatally in the rabbit (4). The calcium sensitivity of myofilaments, however, decreases with development in the rat, chick, and rabbit (5-7); this fall could result from a developmental switch in isoform expression of cTnT, a thin filament protein essential for Ca 2ϩ -regulated force development (8). Expression of cTnT 1 and cTnT 2 falls and that of cTnT 3 and cTnT 4 increases with development in the rabbit.We expressed recombinant rabbit (r)cTnT 1 and rcTnT 4 in Sf9 cells and compared their effects on Ca 2ϩ -binding of isolated troponin in solution and in skinned muscle fibers in vitro. Further, we compared calcium transients and L-type calcium currents (I Ca ) in cardiac myocytes from 3-wk-old rabbits expressing cTnT 1 and from adults that express predominantly cTnT 4 and no cTnT 1 .We found that (a) in solution, Tn comprising cTnT 1 (Tn cTnT1 ) has higher calcium affinity than Tn comprising cTnT 4 (Tn cTnT4 ), (b) fibers reconstituted with cTnT 1 were more sensitive to calcium than those reconstituted with cTnT 4 , and (c) peak [Ca 2ϩ ] i and I Ca were significantly greater in adult than in 3-wk-old myocytes. Our data provide no evidence that incorporation of Tn into the myofilaments alters Tn-calcium binding affinity.By imparting to the myofilaments a higher calcium sensitivity, the higher expression of cTnT 1 and cTnT 2 in immature myocytes would compensate partially for their smaller [Ca 2ϩ ] i transients. MATERIALS AND METHODSAnimals used in this study were handled according to the animal welfare regulations of Duke University (Durham, NC). The protocol was approved by the Institutional Animal Care and Use Committee. The rabbits were anesthetized (100 mg/kg ketamine and 10 mg/kg xylazine i.p.), and the heart was removed to obtain ventricular muscle fibers or isolated myocytes.Preparation of cTnT. cTnT isoforms were expressed in Sf9 cells using the baculovirus system (Invitrogen). The cDNA of rabbit cTnT 1 (9) was cloned at the EcoR I restriction site into pVL1392 by releas...

show abstract

“…The contacted T cells could be distinguished from L cells under a microscope by their small size. The membrane capacitance was measured using a method described by Huynh and colleagues (26) and showed no difference between control and peptide-stimulated groups (membrane capacitance, 0.81 Ϯ 0.03, and 0.89 Ϯ 0.05 F/cm 2 , respectively). To record the outward currents, IS contained a K ϩ -rich solution as described above.…”

Section: Electrophysiologymentioning

confidence: 99%

An Amiloride-Sensitive and Voltage-Dependent Na+ Channel in an HLA-DR-Restricted Human T Cell Clone

Lai

Chen

Nishimura

et al. 2000

The Journal of Immunology

View full text Add to dashboard Cite

We investigated changes in voltage-gated Na+ currents and effects of extracellular Na+ on proliferation in HLA-DR-restricted human CD4+ αβ T cells after stimulation with a non-self antigenic peptide, M12p54–68. In the absence of antigenic peptide, neither single (n = 80) nor APC-contacted (n = 71) T cells showed voltage-gated inward currents recording with whole-cell patch-clamp techniques, even with Ca2+ and Na+ ions present in the perfusion solution. However, with the same recording conditions, 31% (26 of 84) of APC-contacted T cells stimulated with the antigenic peptide showed voltage-dependent inward currents that were elicited from −60 mV. The inward currents were not inhibited in extracellular Ca2+-free conditions or in the presence of 1 mM NiCl2. However, they were completely inhibited in extracellular Na+-free conditions, which were made by replacing Na+ with iso-osmotic N-methyl-d-glucamine or choline. The Na+ currents were insensitive to tetrodotoxin, a classical blocker of Na+ channels, but were dose-dependently inhibited by amiloride, a potassium-sparing pyrazine diuretic. Furthermore, the Ag-specific proliferative response of T cells was completely inhibited in Na+-free Tyrode’s solution and was suppressed by amiloride in a dose-dependent manner. Our findings suggest that activation of amiloride-sensitive and voltage-gated Na+ channels would be an important step to allow an adequate influx of Na+ and maintain a sustained high Ca2+ level during T cell activation.

show abstract

Developmental changes in membrane Ca2+ and K+ currents in fetal, neonatal, and adult rabbit ventricular myocytes.

Cited by 114 publications

References 30 publications

Expression of ATP-Sensitive K+ Channel Subunits during Perinatal Maturation in the Mouse Heart

Expression of ATP-Sensitive K+ Channel Subunits during Perinatal Maturation in the Mouse Heart

Development and Cardiac Contractility: Cardiac Troponin T Isoforms and Cytosolic Calcium in Rabbit

An Amiloride-Sensitive and Voltage-Dependent Na+ Channel in an HLA-DR-Restricted Human T Cell Clone

Contact Info

Product

Resources

About