Cyclic nucleotide-activated channels in carp olfactory receptor cells.
When applied from the cytoplasmic side, cyclic 3',5'-adenosine and guanosine monophosphates reversibly increased the ion permeability of inside-out patches of carp olfactory neuron plasma membrane. The cAMP (cGMP)-induced permeability via cAMP (cGMP) concentration was fitted by Hill's equation with the exponents of 1.07 +/- 0.15 (1.12 +/- 0.05) and EC50 = 1.3 +/- 0.6 microM (0.9 +/- 0.3 microM). Substitution of NaCl in the bathing solution by chlorides of other alkali metals resulted in a slight shift of reversal potential of the cyclic nucleotide-dependent (CN) current, which indicates a weak selectivity of the channels. Permeability coefficients calculated by Goldman-Hodgkin-Katz's equation corresponded to the following relation: PNa/PK/PLi/PRb/PCs = 1:0.98:0.94:0.70:0.61. Ca2+ and Mg2+ in physiological concentrations blocked the channels activated by cyclic nucleotides (CN-channels). In the absence of divalent cations the conductance of single CN-channels was equal to 51 +/- 9 pS in 100 mM NaCl solution. Channel density did not exceed 1 micron-2. The maximal open state probability of the channel (Po) tended towards 1.0 at a high concentration of cAMP or cGMP. Dichlorobenzamil decreased Po without changing the single CN-channel' conductance. CN-channels exhibited burst activity. Mean open and closed times as well as the burst duration depended on agonist concentration. A kinetic model with four states (an inactivated, a closed and two open ones) is suggested to explain the regularities of CN-channel gating and dose-response relations.
Kolesnikov
S S
SS
Institute of Cell biophysics, Russian Academy of Sciences, Pushchino (Russian Federation).
Kosolapov
A V
AV
D000818:Animals; D002118:Calcium; D002347:Carps / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D007700:Kinetics; D008274:Magnesium; D009712:Nucleotides, Cyclic / Q000378:metabolism*; D018035:Receptors, Odorant
D002352:Carrier Proteins; D009712:Nucleotides, Cyclic; D018035:Receptors, Odorant; C045648:odorant-binding protein; D008274:Magnesium; D002118:Calcium