Stretch‐activated and background non‐selective cation channels in rat atrial myocytes

Abstract

Stretch‐activated channels (SACs) were studied in isolated rat atrial myocytes using the whole‐cell and single‐channel patch clamp techniques. Longitudinal stretch was applied by using two patch electrodes. In current clamp configuration, mechanical stretch of 20 % of resting cell length depolarised the resting membrane potential (RMP) from ‐63·6 ± 0·58 mV (n= 19) to ‐54·6 ± 2·4 mV (n= 13) and prolonged the action potential duration (APD) by 32·2 ± 8·8 ms (n= 7). Depolarisation, if strong enough, triggered spontaneous APs. In the voltage clamp configuration, stretch increased membrane conductance in a progressive manner. The current‐voltage (I–V) relationship of the stretch‐activated current (ISAC) was linear and reversed at ‐6·1 ± 3·7 mV (n= 7). The inward component of ISAC was abolished by the replacement of Na+ with NMDG+, but ISAC was hardly altered by the Cl− channel blocker DIDS or removal of external Cl−. The permeability ratio for various cations (PCs:PNa:PLi= 1·05:1:0·98) indicated that the SAC current was a non‐selective cation current (ISAC,NC). The background current was also found to be non‐selective to cations (INSC,b); the permeability ratio (PCs:PNa:PLi= 1·49:1:0·70) was different from that of ISAC,NC. Gadolinium (Gd3+) acted on INSC,b and ISAC,NC differently. Gd3+ inhibited INSC,b in a concentration‐dependent manner with an IC50 value of 46·2 ± 0·8 μM (n= 5). Consistent with this effect, Gd3+ hyperpolarised the resting membrane potential (‐71·1 ± 0·26 mV, n= 9). In the presence of Gd3+ (0·1 mM), stretch still induced ISAC,NC and diastolic depolarisation. Single‐channel activities were recorded in isotonic Na+ and Cs+ solutions using the inside‐out configuration. In NMDG+ solution, outward currents were abolished. Gd3+ (100 μM) strongly inhibited channel opening both from the inside and outside. In the presence of Gd3+ (100 μM) in the pipette solution, an increase in pipette pressure induced an increase in channel opening (21·27 ± 0·24 pS; n= 7), which was distinct from background activity. We concluded from the above results that longitudinal stretch in rat atrial myocytes induces the activation of non‐selective cation channels that can be distinguished from background channels by their different electrophysiology and pharmacology.

Ionic Currents and Spontaneous Firing in Neurons Isolated from the Cerebellar Nuclei

“…The channels carrying this current may account for the resting permeability to sodium in many cells. The current appears electrophysiologically similar to background nonselective cation currents of cardiac cells (Hagiwara et Manabe et al, 1995;Zhang et al, 2000). The existence of such a flux in cerebellar nuclear neurons is consistent with Jahnsen's (1986a) observation that the cells "always showed signs of having a steady inward current."…”

Drift and breakup of spiral waves in reaction–diffusion–mechanics systems

“…The overall physiological action of these channels is depolarization of the membrane in response to stretch, as shown in the majority of experimental observations from isolated cardiac tissue and the whole heart. Experimental studies of the electrophysiological properties of stretch-activated channels show that they are activated instantly by mechanical stimulation, and the currentvoltage (I-V) relationship for the most important nonspecific cation channel is linear (18,19). On the basis of these observations, linear ionic models for I s have been proposed (20,21).…”

“…In our model, we used values close to E s ϳ 1 to provide the depolarizing effect. However, the exact value of the reversal potential may depend on the cell type (11,18,19); therefore, we performed simulations with lower values of E s to investigate the possible effects on the main results of this study.…”

Regulation of transient receptor potential canonical channel 1 (TRPC1) by sphingosine 1-phosphate in C2C12 myoblasts and its relevance for a role of mechanotransduction in skeletal muscle differentiation

“…The SAC and/or SOC conductance (G m ) given in the results for any experimental conditions was evaluated from I m . In order to reveal the presence of SACs, the cells were stretched using two patch microelectrodes, as previously reported (Zhang et al, 2000). Briefly, one microelectrode was positioned by a hydraulic micromanipulator at the centre of the cell and used for electrophysiological measurements, while the other one was sealed 10-20 μm far, and moved by another hydraulic micromanipulator to stretch the cell.…”