K+ channels in cultured bovine retinal pericytes:: Effects of β-adrenergic stimulation

Retinal pericytes are key cells involved in the regulation of retinal blood flow. The purpose of this work was to identify the K channel population expressed in cultured bovine retinal pericytes and to determine whether beta-adrenergic stimulation alters the activity of these channels. Isolated pericytes were obtained by homogenization and filtration of bovine retina and K+ channels were studied with the whole-cell configuration of the patch-clamp technique on 3-5 passaged pericytes. Pericytes expressed an inward current dependent on extracellular K concentration which was sensitive to micromolar concentrations of barium, a characteristic of an inward-rectifying K+ current. Furthermore, two voltage-dependent outward currents were also observed. Their activation and inactivation properties, as well as their respective sensitivity to 4-aminopyridine and iberiotoxin, were indicative of voltage-sensitive and large-conductance calcium-activated K+ channels (BKCa). Isoproterenol and dibutyryl cyclic adenosine monophosphate enhanced the activity of BKCa without affecting the other potassium currents. In conclusion, bovine retinal pericytes express mainly two outward potassium currents, K-v and BKCa, as well as an inward rectifying K+ current, K-ir. Physiologic stimuli such as an increase in extracellular potassium concentration or beta-adrenergic receptor stimulation enhance the activity of K-ir and BKCa, respectively, suggesting a potential role for these channels in the control of retinal blood flow.