Our goal is to determine how the level of free intracellular calcium, (Ca)i, affects the opening and closing kinetics of several important ionic channels in neurons. The conductances, and corresponding channels, studied will be 1) voltage sensitive calcium conductance or gCa, 2) calcium activated cation conductance or gCATca, 3) calcium activated potassium conductance or gKca. The neurons studied will be identified neurons of Aplysia californica in cell culture. The preparation and species has been chosen because we have evidence from prior studies that the above named conductances are present and are important determinants of excitability in these neurons. Channel kinetics will be measured using patch clamping and single channel analysis techniques. The neurons in culture are more amenable to patch clamping than in situ.
The specific aims are 1) to determine whether increased (Ca)i reduces the probability of opening of calcium channels, 2) to characterize the gCATca channels that seem to be present on the majority of Aplysia neurons, and 3) to determine how many subtypes of gKca channels are found on these neurons and how they differ in their kinetics and sensitivity to tetraethylammonium ion. This informaton may help clarify how (Ca)i regulates neuronal excitability. This knowledge could have applications in clinical conditions where effects of calcium on neuronal function are believed to be relevant such as epilepsy and anoxic-ischemic damage.
