Neurons from neonatal hypertensive rats exhibit abnormal membrane properties in vitro

The in vitro membrane properties of neurons from superior cervical ganglia (SCG) of neonatal spontaneously hypertensive (SH), Wistar-Kyoto (WKY), and Sprague-Drawley (SD) rats were studied with microelectrodes. Neurons were obtained by enzymatic dissociation, plated, irradiated, and studied after 2-5 wk. Most SH neurons showed multiple action potentials in response to an intracellular long-duration depolarizing pulse (multiple firing), whereas most neurons from WKY or SD rats generated only one or two action potentials. Multiple firing was inhibited by low concentrations of cobalt (10^-5 M) but not by tetrodotoxin (TTX) (3 x 10^-6 M). Neither high calcium (5-10 x 10^-3 M) nor the Ca²⁺-channel opener Bay K 8644 (10^-6 M) could induce muliple firing in SD or WKY neurons. However, multiple firing was readily induced by apamin (10^-6 M) or tetraethylammonium chloride (5 x 10^-3 M) (Ca²⁺-activated K⁺-channels blockers), with cobalt and TTX sensitivities similar to native multiple-firing neurons. We conclude that 1) multiple firing is characteristic for neonate SH rats SCG neurons in vitro and depends on regenerative Ca²⁺ currents; 2) multiple firing in SH neurons results from a lack of activation of a Ca²⁺ -activated K⁺ conductance and not from a lack of internal Ca²⁺ availability; and 3) multiple firing in SCG neurons mirrors a default in K⁺ conductance common to all cells in genetically hypertensive individuals.