Tytgat J, Nilius B, Carmeliet E
Laboratory of Physiology, KU Leuven, Belgium.
J Gen Physiol. 1990 Nov;96(5):973-90. doi: 10.1085/jgp.96.5.973.
Single-channel measurements and whole-cell experiments with the two suction electrode, voltage clamp technique were used to investigate the effects of external and internal proton concentrations on T-type Ca channels in heart muscle cells of the guinea pig. As in the L-type Ca channel, an increase in the external proton concentration decreases T-type currents, while external alkalinization enlarges the currents. In contrast to the L-type Ca channel, however, a change in the internal proton concentration does not modulate T-type Ca currents. The T-type Ca channel is much more sensitive to variations in pHo than the L-type Ca channel. By the combination of single-channel and whole-cell experiments we can conclude that the observed changes in macroscopic currents are due to (a) changes in the single-channel conductance and in the probability of the T-type Ca channel being open, and (b) the titration of the negative surface charges in the neighborhood of the T-type Ca channel with shifts of both the activation and inactivation processes of the channel. The pHo-induced changes in the maximal conductance (gmax) of the T-type Ca channel show an apparent pKa in the range of 7.1-7.5, while the titration of the negative surface charges near the channel shows an apparent pKa of 7.1 with a concomitant surface potential of -24.6 mV at 5.4 mM [Ca]o. These pKa values, less acid than the pKa values found for the pHo-induced, L-type Ca channel modulation, might imply a physiological importance of this novel type of channel modulation.
采用双吸电极电压钳技术进行单通道测量和全细胞实验，以研究细胞外和细胞内质子浓度对豚鼠心肌细胞T型钙通道的影响。与L型钙通道一样，细胞外质子浓度增加会降低T型电流，而细胞外碱化则会增大电流。然而，与L型钙通道不同的是，细胞内质子浓度的变化并不会调节T型钙电流。T型钙通道对细胞外pH值变化的敏感性远高于L型钙通道。通过单通道和全细胞实验相结合，我们可以得出结论，宏观电流的变化是由于：（a）单通道电导和T型钙通道开放概率的变化；（b）T型钙通道附近负表面电荷的滴定，同时伴随着通道激活和失活过程的移位。细胞外pH值诱导的T型钙通道最大电导（gmax）变化在7.1 - 7.5范围内呈现明显的pKa值，而通道附近负表面电荷的滴定在5.4 mM [Ca]o时呈现7.1的明显pKa值，伴随的表面电位为 -24.6 mV。这些pKa值比细胞外pH值诱导的L型钙通道调制的pKa值酸性弱，这可能意味着这种新型通道调制具有生理重要性。
