McKinley D, Meissner G
J Membr Biol. 1978 Dec 15;44(2):159-86. doi: 10.1007/BF01976037.
Potassium and sodium cation permeabilities of skeletal sarcoplasmic reticulum vesicles were characterized by means of 3H-choline, 22Na+ and 86Rb+ isotope efflux and membrane potential measurements. Membrane potentials were generated by diluting K gluconate filled sarcoplasmic reticulum vesicles and liposomes into Tris or Na gluconate media, in the presence or absence of valinomycin, and were measured using the voltage-sensitive membrane probe 3,3'-dipentyl-2,2'-oxacarbocyanine. About 2/3 of the sarcoplasmic reticulum vesicles, designated Type I, were found to be permeable to Rb+, K+ and Na+. The remaining 1/3, Type II vesicles, were essentially impermeable to these ions. The two types of vesicles were impermeable to larger cations such as choline or Tris. Both were present in about the same ratio in fractions derived from different parts of the reticulum structure. Studies with cations of different size and shape suggested that in Type I vesicles permeation was restricted to molecules fitting through a pore with a cross-section of 4--5 A by 6 A or more. When vesicles were sonicated, vesicles permeable to K+ decreased more than those impermeable to K+. These data suggest the existence of K+, Na+ permeable channels which are probably randomly dispersed in the intact reticulum structure at an estimated density of 50 pores/micrometer2. The function of the channel may be to allow rapid K+ movement to counter Ca2+ fluxes during muscle contraction and relaxation.
通过³H-胆碱、²²Na⁺和⁸⁶Rb⁺同位素外流以及膜电位测量来表征骨骼肌肌质网囊泡的钾离子和钠离子阳离子通透性。在存在或不存在缬氨霉素的情况下，将填充有葡萄糖酸钾的肌质网囊泡和脂质体稀释到Tris或葡萄糖酸钠培养基中产生膜电位，并使用电压敏感膜探针3,3'-二戊基-2,2'-氧杂羰花青进行测量。发现约2/3的肌质网囊泡（称为I型）对Rb⁺、K⁺和Na⁺具有通透性。其余1/3，即II型囊泡，基本上对这些离子不通透。这两种类型的囊泡对较大的阳离子如胆碱或Tris不通透。在源自网状结构不同部分的组分中，两者的比例大致相同。对不同大小和形状阳离子的研究表明，在I型囊泡中，通透作用仅限于适合通过横截面为4 - 5埃×6埃或更大的孔的分子。当对囊泡进行超声处理时，对K⁺通透的囊泡比不通透K⁺的囊泡减少得更多。这些数据表明存在K⁺、Na⁺通透通道，这些通道可能以估计50个孔/微米²的密度随机分散在完整的网状结构中。该通道的功能可能是在肌肉收缩和舒张过程中允许K⁺快速移动以对抗Ca²⁺通量。
