The Properties And Temperature Sensitivities Of L-type Ca～(2+)channel In Hypothalamic Neurons

Ca2~ are perhaps the most versatile ions in the nervous system. It takes part in many physiological and biochemical processes in cells, theryby affects and regulates many cellular fuctions. As the major passway of ca2~ influx, Ca2~ channels participate directly in producing and conducting electrical signals, play an important role in regulating cellular functions. Studies have 2+ showed ca channels are very sensitive to temperature. Hypothalamus is the centre of temperature regulation, neurons in this part have sensitivity to temperature. Ca2~ channels act as a part of the signal transduction passway, what roles do they play in the temperature sensitiviy of the hypothalamic neurons? In this study we adopted the Patch-Clamp technique to study the voltage-dependent L-type Ca2~ channels in hypothalamus, to elucidate their physiological and pharmacological properties and discuss their effects on the adaptation to temperature changes. As follows are the main results and conclusions l.The properties of L-type Ca2~channeI in hypothalamic neurons. It exists voltage-dependent L-type Ca2~channel in hypothalamic neurons, the channels have a relativly larger conductance. They are permeable not 3 only to Ca2~ but also to other ions such as Ba2~ and Sr2~ in normal conditions, and the selectivity of the latter is larger than that of Ca2~. The mean unitary slope conductance for L-type Ca2~channel in hypothalamic neurons was 29.5 ?.lpS, the averaged open-time constant( T ~) was O.28ms and the two averaged closed time constants were 2.9lms (T ci) and 53.22ms( T c2). The channels showed sharply voltage dependence, and hardly had time-dependent 2+ inactivation. The activation threshold of L-type Ca channel was approximately between -4OmV---3OmV, the voltage of maximum activation was about 1 O?OmV. 2. Pharmacological properties of L-type Ca2~channel. This study tested the effects of agonist Bay K8644 and antagonist 2+ nifedipine on the L-type Ca2~ehanneI. Bay K8644, a DHP Ca channel agonist, increased the mean open probability of L-type Ca2~channel by prolonging the averaged duration of channel opening (the average open time increases to 1.61 ins), however, Bay K8644 had no effect on the unitary current amplitude and slope conductance, and increased the ensemble averaged current. nifedipine, also DHP, almost decreased the channel activities completely. 3. The temperature sensitivity of L-type Ca2~channel. Raising of temperature had an obvious effect on the activities of single channel. The unitary current amplitude ,the ensemble averaged current, the mean open probability and mean unitary slope conductance of single channel increased distinctly. As the temperature changed from room temperature to 390C, the unitary current amplitude increased from 1 .89pA to 4.2 lpA, the form of opening changed accordingly, multi-order openings obviusly increased. In brief, as the main passway of Ca2~ influx, Ca2~ channels play important role in the cellular physiological frictions. The changes of opening, closure and structure of Ca2~ channels control a series of cellular process. The response of elecrtical...