[Potential-gated currents in isolated spinal cord neurons of the river lamprey Lampetra fluviatilis]

Abstract

Potential-gated currents in the membranes of enzymatically isolated neurons from the lamprey spinal cord were investigated using the whole cell variant of the patch-clamp technique. As it was revealed the main currents underlying action potential (AP) in the dorsal sensory cells as well as in branched cells are inward Na(+)- and outward K(+)-currents. Sodium current has the duration 4-9 ms, it was rapidly activated and inactivated and blocked by TTX. Its activation and inactivation processes can be fit to modified Bolzmann equations. Outward potassium current can be subdivided into at least two components: 1) early transient rapidly inactivated component which was sensitive to 4-AP and 2) later noninactivated more longer one which was sensitive to TEA. Their function as in the other neurons may be to repolarize membranes after AP generation and to provide the interval between APs during rhythmic activity. Ca2(+)-current was investigated using Ba2+ as a divalent carrier. Judging on two different values of the threshold there are two types of the Ca2(+)-channels in the membranes of the lamprey spinal cells. Ba2(+)-current depend not only on the voltage but on the intracellular enzyme systems particularly on the G-proteins, ATP and CP-CPK. Under normal conditions Ca2(+)-current activated during AP is small but it increase up to 5-10 nA when the other voltage-gated currents are blocked. We conclude that lamprey spinal neurons retain after isolation the electrical properties of neurons in the spinal cord. The obtained results have testified that the kinetic and pharmacological properties of the basic currents in the cells under study are close to those in the other vertebrate neurons and these cells are suitable for investigation of neurotransmitter, neuromodulator and pharmacological agents action on voltage- and agonist-gated membrane currents in vertebrate neurons.