Stretch-activated and background non-selective cation channels in rat atrial myocytes.
1. 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. 2. 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). 3. 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. 4. 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 microM (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. 5. 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 microM) strongly inhibited channel opening both from the inside and outside. In the presence of Gd3+ (100 microM) 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. 6. We concluded from the above results that longitudinal stret 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.
Zhang
Y H
YH
Department of Physiology, Seoul National University, College of Medicine, 28 Yonkeun-Dong, Chongno-Ku, Seoul 110-799, Korea.
Youm
J B
JB
Sung
H K
HK
Lee
S H
SH
Ryu
S Y
SY
Ho
W K
WK
Earm
Y E
YE
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D002412:Cations / Q000378:metabolism*; D015638:Cytochalasin D / Q000494:pharmacology; D005682:Gadolinium / Q000494:pharmacology; D006321:Heart / Q000502:physiology; D006325:Heart Atria; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D007477:Ions; D008564:Membrane Potentials / Q000502:physiology; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010812:Physical Stimulation; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000502:physiology
D002412:Cations; D007473:Ion Channels; D007477:Ions; D015638:Cytochalasin D; D005682:Gadolinium