Blockade of gap junction coupling by glycyrrhetinic acids in guinea pig cochlear artery: a whole-cell voltage- and current-clamp study.
OBJECTIVE
Glycyrrhetinic acids (GAs) are widely used as gap junction blockers, but their efficacy and side effects have not been well determined.


METHODS
Whole-cell electrical recordings were made from vascular smooth muscle cells (VSMCs) embedded in or dissociated from, guinea pig cochlear artery segments.


RESULTS
18beta- & 18alpha-GA concentration-dependently increased membrane input resistance (R(in)) of in situ VSMCs, with a maximal input conductance (G(in)=1/R(in)) reduction of 92% & 77% and IC(50) of 2.0 & 4.4 microm, respectively. 18betaGA (30 microM) resulted in a R(in) of 2.2 GOmega and C(in) of 12 pF, comparable to those of freshly dissociated VSMCs (3.1 GOmega & 6.1 pF). The GAs (> or =30 microM) caused a depolarization in VSMCs in situ. In dispersed VSMCs, they both inhibited delayed rectifiers; 18betaGA also activated a non-selective cation conductance while 18alphaGA inactivated a voltage-independent K+-conductance. ACh induced an outward current in VSMCs in situ at -40 mV, with a positive slope I/V relation and a reversal potential near E(K). The ACh-induced current was attenuated by 18beta- & 18alphaGA with an IC(50) of 4.3 & 7.8 microM, respectively.


CONCLUSIONS
18betaGA blocked the vascular gap junctions, achieving a complete electrical isolation of the recorded VSMC at > or =30 microM while causing a mild depolarization by a complex conductance alteration. 18betaGA suppressed the ACh-induced current in VSMC by blocking the myoendothelial gap junction and by a non-junctional action. 18alphaGA at 30-100 microM failed to fully block the gap junctions while exerting side actions.
Guan
B-C
BC
Department of Otolaryngology, Oregon Hearing Research Center, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA.
Si
J-Q
JQ
Jiang
Z-G
ZG
D015761:4-Aminopyridine / Q000494:pharmacology; D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001158:Arteries / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D001685:Biological Factors / Q000378:metabolism; D003051:Cochlea / Q000098:blood supply*; D051668:Delayed Rectifier Potassium Channels / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity; D017629:Gap Junctions / Q000187:drug effects* / Q000502:physiology; D006034:Glycyrrhetinic Acid / Q000031:analogs & derivatives / Q000737:chemistry / Q000494:pharmacology*; D006168:Guinea Pigs; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D024661:Potassium Channels, Inwardly Rectifying / Q000187:drug effects; D019789:Tetraethylammonium / Q000494:pharmacology; D013997:Time Factors
D001685:Biological Factors; D051668:Delayed Rectifier Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; C067410:endothelium-dependent hyperpolarization factor; C119129:18alpha-glycyrrhetinic acid; D019789:Tetraethylammonium; D015761:4-Aminopyridine; D000109:Acetylcholine; D006034:Glycyrrhetinic Acid; D011188:Potassium