Suarez-Kurtz G, Katz G M, Reuben J P
Departamento de Farmacologia, Universidade Federal do Rio de Janeiro, Brazil.
Pflugers Arch. 1987 Oct;410(3):345-7. doi: 10.1007/BF00580289.
The transient or T-type Ca channel currents of voltage-clamped clonal (GH3) pituitary cells were studied after blockade of Na and K channels. Removal of Ca ions from the bathing medium abolished the Ca currents and allowed Na ions to convey current through the transient channels. These Na currents (I Na,t) were activated at threshold potentials of ca. -85 mV, reached peak amplitudes (up to 2,000 pA) at -60 mV, and were 50% inactivated at holding membrane potentials of -110 to -120 mV. The time constant for inactivation of the maximal I Na,t was 12 +/- 2.4 msec (compared with 22.1 =/- 0.85 msec for maximal I Ca,t). The I Na,t was insensitive to tetrodotoxin (1 micron) and to nimodipine (200 nM) but was abolished by 100 micron external [Ca2+]. It is suggested that high affinity Ca binding sites in the channel modulate the ion selectivity and the current flow through T-type Ca channels.
在钠通道和钾通道被阻断后，对电压钳制的克隆（GH3）垂体细胞的瞬时或T型钙通道电流进行了研究。从浴液中去除钙离子可消除钙电流，并使钠离子通过瞬时通道传导电流。这些钠电流（I Na,t）在约-85 mV的阈电位时被激活，在-60 mV时达到峰值幅度（高达2000 pA），并在-110至-120 mV的钳制膜电位下50%失活。最大I Na,t失活的时间常数为12±2.4毫秒（相比之下，最大I Ca,t的时间常数为22.1±0.85毫秒）。I Na,t对河豚毒素（1微摩尔）和尼莫地平（200纳摩尔）不敏感，但被100微摩尔的细胞外[Ca2+]消除。提示通道中的高亲和力钙结合位点调节离子选择性和通过T型钙通道的电流流动。
