Regulation of lens rCx46-formed hemichannels by activation of protein kinase C, external Ca(2+) and protons.
Rodent lens connexin46 (rCx46) formed active voltage-dependent hemichannels when expressed in Xenopus oocytes. Time-dependent macroscopic currents were evoked upon depolarization. The observed two activation time constants were weakly voltage-dependent and in the order of hundreds of milliseconds and seconds, respectively. Occasionally, the macroscopic steady-state current and the corresponding current-voltage curve showed inactivation at high depolarizing voltages (>+50 mV). To account for the fast recovery from inactivation (<2 msec) favored by hyperpolarization, a four-state kinetic model (C(1)(closed) <--> C(2)(closed) <--> O(open) <--> I(inactivated)) is proposed. In the absence of inactivation, the macroscopic conductance decreased and inactivation became visible at voltages positive of +50 mV when the rCx46-expressing oocytes were treated with the protein-kinase-C-activators OAG or TPA, high external concentrations of Ca(2+) or H(+). However, the underlying mechanisms of OAG, H(+) or Ca(2+) action were different. While OAG did not alter the voltage-dependent activation of the rCx46-hemichannels, an increase in the external Ca(2+) or H(+) level shifted the voltage threshold for activation to more positive voltages. In contrast to Ca(2+), protons were not effective in the physiological concentration range. We propose that under physiological conditions only external Ca(2+) and intracellular PKC-dependent processes regulate rCx46 in the lens.
Jedamzik
B
B
Institut für Biophysik, Universität Hannover, Herrenhäuserstr. 2, D-30419 Hannover, Germany.
Marten
I
I
Ngezahayo
A
A
Ernst
A
A
Kolb
H A
HA
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology*; D017630:Connexins / Q000235:genetics / Q000502:physiology*; D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000502:physiology*; D007700:Kinetics; D007908:Lens, Crystalline / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009865:Oocytes / Q000502:physiology; D011493:Protein Kinase C / Q000378:metabolism*; D011522:Protons; D011994:Recombinant Proteins / Q000378:metabolism; D012377:Rodentia; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014982:Xenopus laevis
D017630:Connexins; D007473:Ion Channels; D011522:Protons; D011994:Recombinant Proteins; C082917:GJA3 protein, human; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium