Stimulation of neuronal calcium conductance by parathyroid hormone

The effects of parathyroid hormone (PTH) on voltage-dependent potassium channels at the Helix pomatia neuronal membrane were investigated in voltage-clamped experiments using intracellular perfusion techniques. The hormone was found to produce a 2-stage effect on calcium current (I sub(Ca)). The initial, brief stage of PTH action consisted of a minor increase in I sub(Ca) and was partially reversible. This was followed by the second (slow) stage, developing for 60-70 min, whereupon level of I sub(Ca) doubled. This hormonal action was not easily reversed and did not occur unless the intracellular solution contained ATP or the hormone was applied after perfusing the cell. Introducing EDTA into the perfusate induced a considerable declined in PTH effects. Adding concentrations of exogenous cAMP and cGMP, respectively, did not imitate the action of this hormone.