Figure 7. Effect of changes in frequency of stimulation on 20-HETE-induced activation of L-type Ca²⁺ channel current carried by Ba²⁺ in cat cerebral VSMCs.

A, comparison of macroscopic inward L-type Ca²⁺ currents elicited by 10 repetitive 200 ms step pulses from −70 to +10 mV with frequencies of depolarization of 2 Hz and 0.1 Hz. The magnitudes of inward currents evoked using this depolarizing step pulse at rates of 2 Hz and 0.1 Hz are not significantly different. In both traces arrows 1 and 2 represent the first and last episodes of the voltage step regime, respectively. B, mean percentage of maximum 20-HETE-induced peak current evoked by a depolarizing test pulse from −70 to +10 mV plotted against increased frequency of stimulation. Application of 20-HETE (100 nm) significantly enhanced peak inward L-type Ca²⁺ current independent of increases in the frequency of stimulation from one pulse every 10 s (0.1 Hz) to one pulse every 0.5 s (2 Hz) (n = 3 cells from 3 cats, P < 0.001). Each point represents the mean percentage of maximum peak current of the series of steps from −70 to +10 mV before (open circles) and after (filled circles) stimulation with 100 nm 20-HETE. Filled triangles denote mean percentage of maximum peak current values of the first episode, whereas open triangles show mean percentage of maximum peak current of the last episode of the voltage step regime in either the control or after application of 20-HETE (100 nm). Error bars are embedded within the symbols.