细胞外钠离子浓度对羊浦肯野纤维膜钠泵活动的影响

EFFECTS OF EXTRACELLULAR SODIUM CONCENTRATION ON THE SODIUM-PUMP ACTIVITY IN PURKINJE FIBRES OF SHEEP

采用离子选择电极测量羊浦肯野纤维细胞膜内钠离子活度(^(ai)N_a),细胞间钾离子活度(a^ok)及细胞膜电位(v_m),观察不同浓度低钠,无钙液对其影响,在无钙低钠液中,细胞内Na^+逐出,α~iNa 降低,其变化速率,幅值与[Na]_o 相关,同时也受细胞 a^iNa 初始水平(aiNa(o))的影响。aiNa 下降6min 时的稳态水平与[Na]_o 呈直线正相关,这些结果表明,[Na]_o 降低时,细胞膜钠泵活动加强,细胞内 Na^+逐出增加,其最终结果是使 Na+跨膜梯度维持相对稳定,因而可以认为是 Na^+跨膜梯度而不是单纯的细胞内 Na^+控制膜钠泵活动。在低 Na^+液引起细胞内 Na^+主动逐出增加的同时,细胞膜出现超极化,[Na]_o 愈低,膜超极化程度愈高,从低钠液引起的 a^i_(Na),V_m,α~o_k 变化之间的时程关系看,膜超极化主要由加大的外向泵电流引起,同时发生的细胞间 K^+浓度变化对其也有一定影响。

Intracellular sodium activity(α_Na^i),extracellular potassium activity(α_k^0)andresting membrane potential(V_m)were measured in sheep cardiac Purkinje fibresexposured intermittently to calcium-free solution containing different concentrationsof low sodium.In Ca-free low sodium solution,α_Na^i decreased,the rates and am-plitudes of α_Na^i changes were related to [Na]_0 linearly.The linear correlationbetween the stable values of α_Na^i(α_Na^i(s))at 6th minute of α_Na^i decrease and [Na]_0meant that the amplified active Na^+ extrusion and pump current resulting fromdecreased [Na]_0,kept finally Na^+ gradient across the membrane relatively sta-ble.Hence,it was proposed that it was the Na^+ gradient across the membranebut not the internal Na^+ that regulated the sodium pump activity.The membranehyperpolarization which was incident with the increase of active Na^+ extrusionwas caused mainly by the amplified pump current and embellished by the in-tercellular K^+ depletion and accumula ion simultaneously,which was suggestedby the mutual relation of time courses of changes in α_Na^i,V_m,α_k^0 during the ex-posure of the fibre to 1.3Na Ca-free solution.