Calcium currents in the A7r5 smooth muscle-derived cell line

 
 
 
 

Calcium currents in the A7r5 smooth muscle-derived cell line

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Title: Calcium currents in the A7r5 smooth muscle-derived cell line
Author: Marks, Theodore N
Description: I have studied voltage dependent calcium channels in the A7r5 smooth muscle cell line using electrophysiological and biochemical techniques. A dihydropyridine (DHP) sensitive inward current resembling the 'L'-type calcium current was the dominant current in cells under voltage clamp. Inward currents were blocked by extracellular Cd^2+ (IC50 ∼1 μM), and stimulated (in about half of the cells) by isoproterenol (1 μM) or forskolin (10 μM). A7r5 cells express saturable, high affinity, voltage-sensitive DHP antagonist binding sites. Suspensions of quiescent cells showed changes in resting (Ca^2+) i in response to dihydropyridine agonists and increased K^+. Most confluent cell monolayers showed spontaneous transient elevations in (Ca^2+) i, the frequency and magnitude of which were DHP sensitive. I investigated the gating kinetics of the channels at the level of single channels and whole cell currents, in the absence and presence of DHP calcium channel agonists. Although latencies to first opening and macroscopic currents are strongly voltage dependent, analysis of amplitude histograms indicates that the primary open-closed transition is voltage-independent. This suggests that the molecular mechanisms for voltage-sensing and channel gating are di stinct, but coupled. I propose a modified Monod-Wyman-Changeux (MWC) model for channel activation, where movement of a voltage sensor is analogous to ligand binding, and the closed and open channels correspond to inactivate (T) and active (R) states. This model can account for normal gating behavior of the calcium channel, and is consistent with existing information on ion channel structure. DHP agonists lengthen single channel openings, slow deactivation kinetics, shift the activation curve to more negative potentials with an increase in slope, and reduce the latency to first opening. These effects are predicted by the MWC model, if we make the simple assumption that DHP agonists act as allosteric effectors to stabilize the open state of the channel.
Permanent Link: http://rave.ohiolink.edu/etdc/view?acc_num=case1054919224
http://hdl.handle.net/2374.OX/16232
Date: 1990

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