Effect of Ca²⁺ channel antagonists on MTN survival and on [Ca²⁺]_i. A, Percentages of MTN survival in cultures supplemented with 30K are plotted against different doses of the Ca²⁺ channel antagonists nifedipine (filled circles), verapamil (filled squares), and amiloride (filled triangles). Survival was evaluated 24 hr after treatment. Broken lines show survival of cells in sibling control cultures maintained in MEX or in NE culture medium for the same period of time. Survival values are plotted as the mean ± SEM. B, Effect of extracellular high K⁺ on [Ca²⁺]_i. KCl (30 mm) was added to the culture medium of MTNs at 0 min, and [Ca²⁺]_i was measured 1, 5, and 15 min, and 24 and 48 hr after exposition. C, Effect of the addition of high potassium (* 30K) after 10 min in the presence of 10 μm nifedipine (filled circles) and 10 μm amiloride (filled squares). In B andC [Ca²⁺]_i is plotted as the mean ± SEM, and the broken lines represent the average baseline calcium level in control medium.