The blockade of excitation/contraction coupling by nifedipine in patch-clamped rat skeletal muscle cells in culture

Abstract

The effects of the dihydropyridine derivative, nifedipine, well known as a blocker of calcium channels, were tested on cultured rat myoballs. Membrane currents and contractions were simultaneously recorded by means of the patch-clamp technique and a photoelectric transducing method. High concentrations of nifedipine (5 microM) inhibited the contractile responses and inward calcium current (ICa) elicited by long depolarizations. In the absence of ICa (1.5 mM cadmium in the bath), nifedipine inhibited both the ICa-independent contractile component and the outward current, supposed to depend on the intracellular calcium released during contraction. At low concentrations (0.5 microM) the blocking effects of nifedipine could be strongly enhanced by shifting the membrane potential towards less negative values (-60 mV) for 50 s prior to the test pulse. A blocking effect of nifedipine, at a usually ineffective concentration (0.1 microM), could also be observed when long-lasting (3 min) prepulses to 0 mV were applied from a reference membrane potential of -60 mV. This effect could be relieved by long-lasting cell hyperpolarizations (-90 mV). The blocking effects of nifedipine unrelated to ICa could be interpreted as an action on a molecule (voltage sensor) in the T-tubule membrane involved in the excitation/contraction coupling process and as a preferential binding of the dihydropyridine derivative on the inactivated form of this molecule, favored by the weak negative potentials or long-lasting depolarizations. The results provide data in favor of the existence of strong similarities between the calcium channels and voltage sensors since their operation was inhibited in a voltage-dependent manner by nifedipine.

Endothelium-derived NO, but not cyclic GMP, is required for hypoxic augmentation in isolated porcine coronary arteries

“…As both nifedipine (8) and extracellular calcium depletion do not prevent the hypoxic augmentation, an increased calcium influx cannot not explain the current phenomenon. The lack of significant changes in intracellular calcium levels shown by confocal fluorescence microscopy with hypoxia confirms that it does not augment the influx of the activator ion.…”

Effect ofSecuridaca longepedunculata. (Polygalaceae) Root Extract on Intracellular Calcium Transient in Cultured Rat Skeletal Muscle Cells

“…b) By contrast, the calcium level-increasing effect induced by application of the SL extract could be related to the ryanodine receptor, since in the presence of ryanodine the amplitude of the calcium transient induced by the SL extract was drastically reduced. In this way, two hypotheses could be constructed: 1) the SL extract was able to directly induce calcium release in a way similar to the action of caffeine (Cognard et al, 1993b;Herrmann-Frank et al, 1999); or 2) the voltage-sensing molecules of the voltage-dependent calcium channel (DHP receptors) are involved in excitation-contraction coupling (Rios & Brum, 1987;Cognard et al, 1990). c) This latter hypothesis was tested by blocking the voltage-sensing molecules of the DHP receptors with nifedipine.…”

“…During the course of this study, three compounds were used to address the depolarization=release processes involved in the SL root extract effects. The first of these compounds was nifedipine, a molecule that has been demonstrated to Accepted: April 2006. be a potent inhibitor of charge movements attributed to the voltage-sensing molecules involved in excitation-contraction coupling (ECC) (Rios & Brum, 1987;Cognard et al, 1990). Nifedipine was used to investigate a possible implication of the T-tubule membrane.…”

Role of the sarcoplasmic reticulum in regulating the activity-dependent expression of the glycogen phosphorylase gene in contractile skeletal muscle cells

“…6). DHAP antagonists, including nifedipine, have been shown to reduce or block the contractile force of primary myotube cultures and of skinned muscle fibers (Cognard et al, 1990;Suda, 1995). In myogenic cultures, DHAP antagonists appear to alter primarily the potentialdependent inactivation of voltage sensors in the transverse tubules that are functionally coupled to SR calcium release (Suda, 1995).…”

“…Rmo myotubes (Table 1) DHAP antagonists also have been reported to impede inward calcium currents in myogenic cultures (Cognard et al, 1990;Posterino and Lamb, 1998). Several investigators have proposed that nifedipine increases AChR transcript levels by impeding sarcolemmal Ca 2ϩ influx and that increased Ca 2ϩ influx reduced ␣AChR levels (Klarsfeld et al, 1989;.…”