ウシ培養滑膜表層細胞の興奮性とイオンチャネル

抄録

Synovial lining cells have been identified as B- and A-types with transmission electronmicrographs. To electrophysiologically characterize these two types of cells, we studied, using a patch-clamp, the excitability and ion channels of cultured synovial lining cells from the bovine metacarpophalangeal joint. We made special efforts to collect pure samples of the lining layer for culture and could establish a clean culture system consisting of only synovial lining cells with little contamination originating from the sublining layer. Experiments using the whole-cell recording on 4- and 5-day short-term primary-cultured cells showed that the probable B-cells (E_r≤ca.-40 mV) responded to electrical stimulation with self-regenerative action potentials, but the probable A-cells (E_r=ca.-20 mV) were electrically inexcitable. The B-cells lost their excitability with time in culture. Using singlechannel recording, we identified in both B- and A-cells 4 high-conductance K-channels (170-250 pS) : 1) two types of depolarization-activated and Ca²⁺ -sensitive K-channels with a low rate of opening (I_{K (vd-1)} ) and with a high rate of opening at resting potential (I_{K (vd-2)} ) ; 2) a voltage-independent K-channel (I_{K (vi)} ) ; and 3) a depolarization-inhibited K-channel (I_{K (vh)} ) . There was also one small-conductance (10-20 pS) K-channel (I_{K (s)} ) ; it was voltage-independent, minimally sensitive to Ca²⁺, and highly open at resting potential in the cell-attached mode. This suggests that the cell's resting conductance is attributable mainly to this I_{K (s)} . The present experiments indicate that the B-cell is clearly different from the A-cell in terms of excitablity and the distribution of channels. A speculation on the possible role of ion channels in cell function of the synovial B-cell has been proposed.