GTPγS Activates Calcium Channels in Neonatal Rat Ventricular Cells
It has been reported that G proteins modulate voltage-dependent Ca2+ channels in cardiac muscle. G proteins may activate channels directly (acting on Ca2+ channel proteins) or indirectly (acting through intracellular second messengers, e.g., cAMP) (Brown, 1990). The effect of the G protein activator, GTPγS, on Ca2+ channels in neonatal rat ventricular cells has not been demonstrated. Therefore, the effect of the intracellular application of GTPγS, a non-hydrolyzable analogue of GTP, on Ca2+ channel currents in neonatal rat ventricular cells was investigated. Two types of Ca2+ channels have been described in the cardiac cells (Bean, 1985). One type of Ca2+ channel activates at a low threshold and inactivates very rapidly. This channel is called the low voltage-activated or transient channel (L channel). The other type of Ca2+ channel requires larger depolarization for activation and inactivates slowly. This channel is called the high voltage-activated or long-lasting channel (L channel). Therefore, two protocols were used in this study. In one protocol, cells were held at a membrane potential of -80 mV. Test pulses from this holding potential to more positive potentials evoked inward Ca2+ currents which consisted of two components (T and L channel components).
KeywordsChannel Current Test Pulse Ventricular Cell Activate Calcium Channel Transient Channel
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