EMERGENCE OF A CHLORIDE PERMEABILITY AFTER INTERNAL PERFUSION WITH CALCIUM IN SQUID GIANT-AXONS

In the resting condition, the membrane of the squid giant axon is high ly permeable to K+, and shows large changes in membrane potential foll owing an increase in external or internal K-concentration. When 3-5 mM Ca2+ was applied internally for 3 min, the membrane became highly per meable to Cl- as compared to K+. The permeability ratio P-Cl/P-K was a bout 0.77 in control experiments, rising to a ratio of 5.5 after Ca2administration. The membrane conductance also increased 6-fold over co ntrols. The permeability ratios for other anions, Cl-, F-, methanesulf ate (MS), and HEPES (P-Cl, P-F, P-MS, and P-HEPES) were 1.00, 0.54, 0. 23, and 0.13, respectively.