Identification of Kir2.1 channel activity in cultured trabecular meshwork cells

PURPOSE. To study the presence of inwardly rectifying K+ (Kir) channels in cultured bovine (BTM) and human (HTM) trabecular meshwork cells. METHODS. Cultures of BTM and HTM cells were obtained by an extracellular ma trix digestion technique. Whole-cell patch-clamp recordings of BTM cells we re performed with the appropriate solutions to detect K+ currents. Also, We stern blot analysis of Kir2.1 protein expression was performed on both cult ured BTM and HTM cells. RESULTS. A strong inwardly rectifying current at negative potentials to the equilibrium potential for K+ (EK+) and highly selective for K+ was detecte d in 60% of cultured BTM cells. The slope conductance of the in-ward rectif ication was more pronounced when the extracellular [K+] was increased and w as proportional to [K+](0.45). The current was blocked by Ba2+ and Cs+ in a voltage- and concentration-dependent manner, with K-d at 0 mV, of 74.7 muM and 45.6 mM, respectively. Current amplitude was reduced by increasing ext racellular [Ca2+]. The current was insensitive to 10 muM glibenclamide and 10 nM tertiapin. The application of 100 muM 8-Br-cAMP reduced the current b y 50%. Kir2.1 channel expression was detected in confluent monolayers of BT M and HTM cells by Western blot analysis. CONCLUSIONS. A population of cultured BTM cells expressed an inwardly recti fying K+ current that illustrates the biophysical and pharmacologic charact eristics of the detected Kir2.1 channel protein. Kir2.1 channels are also t hought to be present in HTM cells. Kir2.1 channels could be related to TM p hysiology, because they are involved in contractile and cell volume regulat ory responses, two mechanisms that modify TM permeability.