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-Dawley (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 multiple 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 of 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.