Inhibition of heart calcium and chloride currents by sodium iodide. Specific attenuation in cAMP-dependent protein kinase-mediated regulation.

Abstract

The enzymes cAMP-dependent protein kinase (PKA) and protein kinase C (PKC) regulate the activity of cardiac ion channel proteins. In this study the whole-cell arrangement of the patch clamp technique was used to examine the effect of NaI on PKA-stimulated CI-and Ca 2+ channels in isolated guinea pig ventricular myocytes. CI-currents (lcl) activated either by the 13-adrenergic agonist isoproterenol or the membrane-soluble cAMP analogue, 8-chlorphenylthio (8-CPT) cAMP, were greatly reduced in amplitude after substitution of an external solution containing 140 mM NaCI with a solution containing 140 mM NaI. This reduction was accompanied by a shift of -7 mV in the reversal potential (E,~) for Icl and could be reversed upon return to the NaCI external solution. Inhibition of Io by NaI occurred in a concentration-dependent manner and was more pronounced for inward Io (ICs0 = 19 mM at -60 mV) than for outward Ict (ICs0 = 60 mM at +60 mV). In contrast to Icl activated by PKA, lcl activated by PKC was slightly augmented in the presence of NaI and the E,~v was found to shift by -15 mV. Based on these data, the relative permeability of I-to C1-(Pl/Pcl) for this channel was calculated to be 1.79. NaI produced no change in the amplitude of inward calcium currents (/ca) recorded under basal conditions, but strongly inhibited/ca augmented by isoproterenol and 8-CPT cAMP, and during dialysis of cells with the catalytic subunit of PKA (CS). The in vitro incorporation of [~/-s2P]ATP into histone IIA and Kemptide, measured in the presence of PKA and cAMP, was not significantly different in assay mixtures containing salts of CI-and I-. However, the ability of isoproterenol to augment basal/ca in whole-cell experiments was attenuated when experiments were carried out entirely in NaI external solution. Thus, the reduction in Io and lca observed in this study may result from a direct effect of I-on the phosphorylation/ dephosphorylation of cardiac ion channel proteins or associated regulatory proteins.Address reprint requests to Dr.

On the mechanism of rectification of the isoproterenol-activated chloride current in guinea-pig ventricular myocytes.

“…This is consistent with the findings of the present study, which show that the selectivity sequence of the ISO-activated CIchannel in cardiac myocytes is the same as that for CFTR: Br-> CI-> I- . However, our results differ from another report that found I-to be more permeant than CI-in a cAMP-dependent CI-channel in cardiac myocytes (Walsh and Long, 1992).…”

“…Recently, interest in cardiac CI-channels has been rekindled by the discovery of several, potentially separate, C1-conductances in cardiac myocytes. These include an autonomically regulated CI-current found in guinea-pig and rabbit ventricular myocytes (Harvey and Hume, 1989a, b;Bahinski, Nairn, Greengard, and Gadsby, 1989); a Ca2÷-activated CI-current found in rabbit atrial and ventricular myocytes Gibbons, 1991, 1992); a CI-current activated by swelling in canine cardiac cells (Sorota, 1992;Tseng, 1992); a CI-current activated by protein kinase C in guinea-pig ventricular myocytes (Walsh, 1991;Walsh and Long, 1992); and a C1current activated by purinergic agonists in guinea-pig atrial cells (Matsuura and Ehara, 1992). To completely appreciate the role of CI-channels in the regulation of cardiac function, it will be important to fully describe the biophysical characteristics of the channels activated through each of the different pathways described above.…”

Influence of Infrasound Exposure on the Whole L-type Calcium Currents in Rat Ventricular Myocytes

“…Cardiomyocytes were enzymatically isolated from adult rat left ventricular tissues using a previously described method [9]. In brief, hearts were rapidly excised and perfused via coronary artery with a normal Tyrode's solution for 2-3 min, followed by a Ca 2?…”

“…The procedures for current measurement and analysis were described in detail previously [9,11]. Pipettes were made from the Prism glass capillaries (Dagan Corp.) with a resistance of 1-2 XX.…”

Arylaminobenzoate Block of the Cardiac Cyclic AMP-Dependent Chloride Current

“…The external application of 2 M forskolin caused the activation of a time-independent, outward-rectifying Cl Ϫ current when recorded with a Cl Ϫ concentration of 76 mM in the pipette and 146 mM in the bath (E Cl ϭ Ϫ16 mV). The physiological properties of this cardiac I Cl have been described previously (Bahinski et al, 1989;Harvey and Hume, 1989a;Matsuoka et al, 1990;Walsh and Long, 1992). As shown in Fig.…”