Two distinct inactivation processes related to phosphorylation in cardiac L-type Ca²⁺ channel currents

Abstract

We investigated the inactivation process of macroscopic cardiac L-type Ca(2+) channel currents using the whole cell patch-clamp technique with Na(+) as the current carrier. The inactivation process of the inward currents carried by Na(+) through the channel consisted of two components >0 mV. The time constant of the faster inactivating component (30.6 +/- 2.2 ms at 0 mV) decreased with depolarization, but the time constant of the slower inactivating component (489 +/- 21 ms at 0 mV) was not significantly influenced by the membrane potential. The inactivation process in the presence of isoproterenol (100 nM) consisted of a single component (538 +/- 60 ms at 0 mV). A protein kinase inhibitor, H-89, decreased the currents and attenuated the effects of isoproterenol. In the presence of cAMP (500 microM), the inactivation process consisted of a single slow component. We propose that the faster inactivating component represents a kinetic of the dephosphorylated or partially phosphorylated channel, and phosphorylation converts the kinetics into one with a different voltage dependency.

Mechanisms of L-Type Ca 2+ Current Downregulation in Rat Atrial Myocytes During Heart Failure

“…30 Indeed, as in other species and myocyte types, [31][32][33] the I Ca of rat atrial myocytes is highly sensitive to phosphatase inhibition; these enzymes appear to play an important role in the basal regulation of the current, keeping with the tight coupling between Ca 2ϩ channels and OA-sensitive phosphatases. 34 Various studies have shown that the kinetics of I Ca inactivation also depend on cAMPdependent regulation of the current 35,36 and the slowly decaying I Ca in HF may be another consequence of its downregulation. However, other mechanisms may explain the slow rate of I Ca inactivation in atrial myocytes from HF.…”

Functional Expression and Inactivation of L-type Ca²⁺ Currents During Murine Heart Development -Implications for Cardiac Ca²⁺ Homeostasis

“…* indicates statistical significance. To test whether there might be a development-dependent difference in the amount of current, which is inactivated, we studied the steady-state inactivation at the isochronic state [4,6] as well as the time-and voltage-dependence of inactivation. Fig.…”

“…Although earlier studies could not demonstrate a large quantitative impact of VDI on the inactivation process in general, recent studies analyzed this aspect in more detail. VDI strongly increased with depolarisation and was fast at positive membrane potentials [4,7].…”

“…In general, the contribution of CDI and VDI to the decay of I CaL is determined by depolarization of the cell or by phosphorylation of the L-type Ca 2+ channel protein [4][5][6][7]. The close relationship of L-type Ca 2+ channels with the Ca 2+ extrusion mechanisms of the sarcoplasmatic reticulum (SR), formed by T-tubuli and ryanodine receptors (RyRs), significantly contribute to the CDI process due to a strong increase of local subsarcolemmal [Ca 2+ ] i during the CICR process [8,9].…”

Lysophosphatidylcholine Augments Ca_v3.2 but Not Ca_v3.1 T-Type Ca²⁺ Channel Current Expressed in HEK-293 Cells

“…The actions of protein kinases were inhibited by H-89 (protein kinase A, PKA, inhibitor), chelerythrine (PKC inhibitor), KT 5823 (protein kinase G, PKG, inhibitor), KN-62 (calmodulin kinase II inhibitor) or PD 98059 (extracellular signal-regulated kinase 1/2 inhibitor) at the concentration of 5-10 times the ones inducing a 50% inhibition (IC 50 ) of these protein kinases [9,[20][21][22][23] . These chemicals were dissolved in dimethyl sulfoxide (DMSO), where the fi nal concentration of DMSO was ^ 0.1%.…”