Primary and adaptive changes of A-type K+ currents in sympathetic neurons from hypertensive rats.

The A-type K+ current (IA) of superior cervical ganglion neurons acutely isolated from spontaneously hypertensive (SHR) and age-matched Wistar-Kyoto (WKY) rats was compared under whole cell voltage clamp. Activation parameters were similar in each strain. Steady-state inactivation was shifted approximately -6 mV in SHR, where one-half inactivation occurred at -81 mV vs. -75 mV in WKY rats. The shift was not present in prehypertensive SHR but remained in adult enalapril-treated SHR and, therefore, may represent a primary alteration of IA properties. IA amplitudes evoked from physiological potentials were similar, despite inactivation of a greater fraction of the current in the SHR. Comparing maximal IA densities revealed that current density is elevated in the SHR, which compensates for the inactivation shift. Current density decreased with age in WKY neurons but did not significantly decline in SHR neurons unless hypertension was prevented with enalapril. Thus adult SHR neurons may retain a high IA density as an adaptive response to offset potential hyperexcitability resulting from the hyperpolarized IA inactivation.