Wallfelt C, Larsson R, Johansson H, Rastad J, Akerström G, Ljunghall S, Gylfe E
Acta Physiol Scand. 1985 Jun;124(2):239-45. doi: 10.1111/j.1748-1716.1985.tb07657.x.
Pieces of rat parathyroid glands were used to study fluxes of 45Ca and 86Rb. The uptake of 45Ca increased with the extracellular Ca2+ concentration up to at least 5 mM. A rise of extracellular Ca2+ had dual effects on 45Ca efflux in terms of an initial stimulation and a subsequent inhibition. However, K+ depolarization neither affected the uptake nor the efflux of 45Ca indicating a lack of voltage-dependent Ca2+ channels. The depolarization obtained with exposure to Ca2+ cannot be attributed to a decreased K+ permeability, since the 86Rb concentrating ability diminished and the efflux of the isotope increased when parathyroid pieces were exposed to a raised Ca2+ concentration. A stimulation of 86Rb efflux by the Ca2+ ionophore A-23187 indicated that the parathyroid cells possess a K+ permeability activated by cytoplasmic Ca2+. It is suggested that Ca2+ fluxes through channels sensitive to activation by Ca2+ are important both for the membrane potential and the cytoplasmic Ca2+ activity.
采用大鼠甲状旁腺组织块研究了⁴⁵Ca和⁸⁶Rb的通量。⁴⁵Ca的摄取量随细胞外Ca²⁺浓度增加，至少在5 mM时仍会增加。细胞外Ca²⁺升高对⁴⁵Ca外流有双重作用，即先是刺激，随后是抑制。然而，K⁺去极化既不影响⁴⁵Ca的摄取，也不影响其外流，这表明不存在电压依赖性Ca²⁺通道。暴露于Ca²⁺时出现的去极化不能归因于K⁺通透性降低，因为当甲状旁腺组织块暴露于升高的Ca²⁺浓度时，⁸⁶Rb的浓缩能力减弱且该同位素的外流增加。Ca²⁺离子载体A - 23187刺激⁸⁶Rb外流表明甲状旁腺细胞具有由细胞质Ca²⁺激活的K⁺通透性。提示通过对Ca²⁺激活敏感的通道的Ca²⁺通量对膜电位和细胞质Ca²⁺活性均很重要。
