Figure 5.

The effect of different external [K⁺] on Sr²⁺-induced repetitive [Ca²⁺]_cy spikes and repetitive transient hyperpolarizations. A, Repetitive [Ca²⁺]_cy spikes (bottom) and repetitive transient hyperpolarizations (E/mV, top) were induced by the addition of 1 mm SrCl₂ to the medium. The external [K⁺] was increased from 0.1 mm KCl (standard medium) to 1 mm, to 10 mm, and finally to 100 mm (bars on top). Sampling frequency was 1/3 s⁻¹. B, The amplitude of the transient hyperpolarizations (E/mV) was plotted against the logarithm of the external [K⁺]: log ([K⁺]_ex/M). A linear regression analysis (solid line, r = 0.999) yielded a slope of 53.8 ± 0.4 mV for each 10-fold increase in [K⁺]. Data points are given as means ± se (n = 15) with se being smaller than the symbol size.