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A patch‐clamp study of K + ‐channel activity in bovine isolated tracheal smooth muscle cells
Author(s) -
Green K.A.,
Foster R.W.,
Small R.C.
Publication year - 1991
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1991.tb12269.x
Subject(s) - patch clamp , smooth muscle , channel (broadcasting) , chemistry , biophysics , anatomy , electrophysiology , biology , medicine , endocrinology , computer science , telecommunications
1 Single smooth muscle cells were isolated from bovine trachealis by enzymic digestion. The properties of large conductance plasmalemmal K + ‐channels in these cells were studied by the patch‐clamp recording technique. 2 Recordings were made from inside‐out plasmalemmal patches when [K + ] was symmetrically high (140 m m ) and when [Ca 2+ ] on the cytosolic side of the patch was varied from nominally zero to 10 μ m . Large unitary currents of both Ca 2+ ‐dependent and ‐independent types were observed. Measured between +20 and +40 mV, the slope conductances of the channels carrying these currents were 249 ± 18 pS and 268 ± 14 pS respectively. 3 Lowering [K + ] on the cytosolic side of the patches from 140 to 6 m m , shifted the reversal potentials of the two types of unitary current from approximately zero to ≫ +40 mV, suggesting that both currents were carried by K + ‐channels. 4 The Ca 2+ ‐dependent and ‐independent K + ‐channels detected in inside‐out plasmalemmal patches could also be distinguished on the basis of their sensitivity to inhibitors (tetraethylammonium (TEA), 1–10 m m ; Cs + , 10 m m ; Ba 2+ , 1–10 m m ; quinidine, 100 μ m ) applied to the cytosolic surface of the patches. 5 Recordings were made from outside‐out plasmalemmal patches when [K + ] was symmetrically high (140 m m ) and when [Ca 2+ ] on the cytosolic side of the patch was varied from nominally zero to 1 μ m . Ca 2+ ‐dependent unitary currents were observed and the slope conductance of the channel carrying these currents was 229 ± 5 pS. 6 Activity of the Ca 2+ ‐dependent K + ‐channel detected in outside‐out patches could be inhibited by application of TEA (1 m m ), Cs + (10 m m ), Ba 2+ (10 m m ) or quinidine (100 μ m ) to the external surface of the patch. 4‐Aminopyridine (4‐AP; 1 m m ) was ineffective as an inhibitor. 7 The activity of the Ca 2+ ‐dependent K + ‐channel recorded from outside‐out patches was reversibly inhibited by charybdotoxin (100 n m ). 8 When whole‐cell recording was performed, the application of a depolarizing voltage ramp evoked outward current which was dependent on the [Ca 2+ ] in the recording pipette and which could be reversibly inhibited by charybdotoxin (50 n m –1 μ m ) applied to the external surface of the cell. 9 We conclude that bovine trachealis cells are richly endowed with charybdotoxin‐sensitive, large conductance, Ca 2+ ‐dependent K + ‐channels. These channels carry most of the outward current evoked by a depolarizing ramp and could play a major role in determining the outward rectifying properties of the trachealis cells. The role of the large Ca 2+ ‐independent K + ‐channels remains unclear.