Three types of calcium channels in the membrane of mouse sensory neurons

Three types of electrically-operated calcium channels have been identified in the membrane of cultured dorsal root ganglion neurons from mouse embryos using patch clamp technique. Low-threshold inactivating (LTI) channels with the lowest unitary conductance (5.7 pS with 60 mM Sr2+ or 7.2 pS with 60 mM Ba2+) preserved their activity for a long time on excised membrane patches and were insensitive to dihydropyridine Ca channel agonist Bay K8644. Corresponding whole-cell current could be decreased by 40% with 25 microM D-600. High-threshold inactivating (HTI) channels had somewhat higher unitary conductance (7 pS and 11.4 pS for Sr2+ or Ba2+ at 60 mM concentration) and were much more dependent upon intracellular metabolic support. D-600 inhibited the corresponding HTI whole-cell current by about 10%. High-threshold non-inactivating (HTN) channels were the most conducting ones (9 pS and 18.4 pS for 60 mM Sr2+ or 60 mM Ba2+) and their functioning was strongly metabolic dependent. Whole-cell HTN current could be slightly enhanced by 10 microM Bay K8644 due to some prolongation of channel mean open time. Effect of Bay K8644 was much less pronounced than that reported for cardiac cells. HTN whole-cell current could be almost completely blocked by 25 microM D-600. The described three types of calcium channels revealed different potential dependence and absolute values of mean channel open time.