Overexpression of the Sarcolemmal Calcium Pump in the Myocardium of Transgenic Rats

Abstract

Abstract-The plasma membrane calmodulin-dependent calcium ATPase (PMCA) is a calcium-extruding enzyme controlling Ca 2ϩ homeostasis in nonexcitable cells. However, its function in the myocardium is unclear because of the presence of the Na ϩ /Ca 2ϩ exchanger. We approached the question of the physiological function of the calcium pump using a transgenic "gain of function" model. Transgenic rat lines carrying the human PMCA 4 cDNA under control of the ventricle-specific myosin light chain-2 promoter were established, and expression in the myocardium was ascertained at the mRNA, protein, and functional levels. In vivo hemodynamic measurements in adult homozygous animals showed no differences in baseline and increased cardiac performance recruited by volume overload compared with controls. No differences between transgenic and control cardiomyocytes were found in patch clamp voltage dependence, activation/inactivation behavior of the L-type Ca 2ϩ current, or fast [Ca 2ϩ ] i transients (assessed by the Fura-2 method). To test whether the PMCA might be involved in processes other than beat-to-beat regulation of contraction/relaxation, we compared growth processes of neonatal transgenic and control cardiomyocytes. A 1.6-and 2.3-fold higher synthesis rate of total protein was seen in cells from transgenic animals compared with controls on incubation with 2% FCS for 24 hours and 36 hours, respectively. An effect of similar magnitude was observed using 20 mol/L phenylephrine. A 1.4-fold-and 2.0-fold-higher protein synthesis peak was seen in PMCA-overexpressing cardiomyocytes after stimulation with isoproterenol for 12 hours and 24 hours, respectively. Because pivotal parts of the ␣-and ␤-adrenergic signal transduction pathways recently have been localized to caveolae, we tested the hypothesis that the PMCA might alter the amplitude of ␣-and ␤-adrenergic growth signals by virtue of its localization in caveolae. Biochemical as well as immunocytochemical studies suggested that the PMCA in large part was colocalized with caveolin 3 in caveolae of cardiomyocytes. These results indicate that the sarcolemmal Ca 2ϩ -pump has little relevance for beat-to-beat regulation of contraction/relaxation in adult animals but likely plays a role in regulating myocardial growth, possibly through modulation of caveolar signal transduction. (Circ Res. 1998;83:877-888.)

Ca2+ clearance in smooth muscle: lessons from gene-altered mice

“…Due to their widespread distribution, they are thought to be important "housekeeping" Ca 2+ -pumps, but their function in smooth muscle is less well known. In addition to Ca 2+ homeostasis, it has been suggested that PMCA is associated with vascular smooth muscle proliferation (Abramowitz et al, 2000) and signal transduction (Hammes et al, 1998). The latter is based on the PDZ domains in PMCA4b which lead to a complex with nitric oxide synthase I in caveolae of vascular smooth muscle (Schuh et al, 2001).…”

Calcineurin in Human Heart Hypertrophy

“…Further processing was according to standard procedures. 7 Protein was visualized with the ECL detection system (Amersham Pharmacia Biotech). Signals were quantified with ScanPack (Biometra).…”

Interaction of the Plasma Membrane Ca2+ Pump 4b/CI with the Ca2+/Calmodulin-dependent Membrane-associated Kinase CASK

“…Recently, a role of the carboxyeosin-sensitive Ca 2ϩ -ATPase PMCA in controlling resting [Ca 2ϩ ] i and the reduction in [Ca 2ϩ ] i after an increase in [Ca 2ϩ ] i in rat ventricular myocytes has been demonstrated (12). In contrast to these observations, overexpression of PMCA4b in the myocardium of transgenic rats did not result in an altered regulation of contraction/relaxation cycle but in an enhanced growth response of cardiac myocytes to different stimuli (13). Additionally, it has been shown that the C termini of several PMCA variants, especially variants PMCA4b and PMCA2b, bind to PDZ domains of proteins of the MAGUK (membrane-associated guanylate kinases) family (14,15), to the PDZ domain of nitricoxide synthase I (nNOS, NOS-I (16)) and to Na ϩ /H ϩ exchanger regulatory factor (NHERF (23)).…”