Single-channel and [3H]ryanodine binding experiments were carried out to examine the effects of imperatoxin activator (IpTxa), a 33 amino acid peptide isolated from the venom of the African scorpion Pandinus imperator, on rabbit skeletal and canine cardiac muscle Ca2+ release channels (CRCs). Single channel currents from purified CRCs incorporated into planar lipid bilayers were recorded in 250 mM KCl media. Addition of IpTxa in nanomolar concentration to the cytosolic (cis) side, but not to the lumenal (trans) side, induced substates in both ryanodine receptor isoforms. The substates displayed a slightly rectifying current–voltage relationship. The chord conductance at −40 mV was ∼43% of the full conductance, whereas it was ∼28% at a holding potential of +40 mV. The substate formation by IpTxa was voltage and concentration dependent. Analysis of voltage and concentration dependence and kinetics of substate formation suggested that IpTxa reversibly binds to the CRC at a single site in the voltage drop across the channel. The rate constant for IpTxa binding to the skeletal muscle CRC increased e-fold per +53 mV and the rate constant of dissociation decreased e-fold per +25 mV applied holding potential. The effective valence of the reaction leading to the substate was ∼1.5. The IpTxa binding site was calculated to be located at ∼23% of the voltage drop from the cytosolic side. IpTxa induced substates in the ryanodine-modified skeletal CRC and increased or reduced [3H]ryanodine binding to sarcoplasmic reticulum vesicles depending on the level of channel activation. These results suggest that IpTxa induces subconductance states in skeletal and cardiac muscle Ca2+ release channels by binding to a single, cytosolically accessible site different from the ryanodine binding site.
Skip Nav Destination
Article navigation
1 May 1998
Article|
May 01 1998
Imperatoxin A Induces Subconductance States in Ca2+ Release Channels (Ryanodine Receptors) of Cardiac and Skeletal Muscle
Ashutosh Tripathy,
Ashutosh Tripathy
From the *Department of Biochemistry and Biophysics, and Department of Physiology, University of North Carolina, Chapel Hill, North Carolina 27599; and ‡Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin 53706
Search for other works by this author on:
Wolfgang Resch,
Wolfgang Resch
From the *Department of Biochemistry and Biophysics, and Department of Physiology, University of North Carolina, Chapel Hill, North Carolina 27599; and ‡Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin 53706
Search for other works by this author on:
Le Xu,
Le Xu
From the *Department of Biochemistry and Biophysics, and Department of Physiology, University of North Carolina, Chapel Hill, North Carolina 27599; and ‡Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin 53706
Search for other works by this author on:
Hector H. Valdivia,
Hector H. Valdivia
From the *Department of Biochemistry and Biophysics, and Department of Physiology, University of North Carolina, Chapel Hill, North Carolina 27599; and ‡Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin 53706
Search for other works by this author on:
Gerhard Meissner
Gerhard Meissner
From the *Department of Biochemistry and Biophysics, and Department of Physiology, University of North Carolina, Chapel Hill, North Carolina 27599; and ‡Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin 53706
Search for other works by this author on:
Ashutosh Tripathy
From the *Department of Biochemistry and Biophysics, and Department of Physiology, University of North Carolina, Chapel Hill, North Carolina 27599; and ‡Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin 53706
Wolfgang Resch
From the *Department of Biochemistry and Biophysics, and Department of Physiology, University of North Carolina, Chapel Hill, North Carolina 27599; and ‡Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin 53706
Le Xu
From the *Department of Biochemistry and Biophysics, and Department of Physiology, University of North Carolina, Chapel Hill, North Carolina 27599; and ‡Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin 53706
Hector H. Valdivia
From the *Department of Biochemistry and Biophysics, and Department of Physiology, University of North Carolina, Chapel Hill, North Carolina 27599; and ‡Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin 53706
Gerhard Meissner
From the *Department of Biochemistry and Biophysics, and Department of Physiology, University of North Carolina, Chapel Hill, North Carolina 27599; and ‡Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin 53706
Address correspondence to Ashutosh Tripathy, Ph.D., Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7260. FAX: 919-966-2852; E-mail: [email protected]
The authors express their appreciation to Dan Pasek for carrying out the [3H]ryanodine binding experiments and Ling Gao for help with the GCG program.
Received:
September 03 1997
Accepted:
March 10 1998
Online ISSN: 1540-7748
Print ISSN: 0022-1295
1998
J Gen Physiol (1998) 111 (5): 679–690.
Article history
Received:
September 03 1997
Accepted:
March 10 1998
Citation
Ashutosh Tripathy, Wolfgang Resch, Le Xu, Hector H. Valdivia, Gerhard Meissner; Imperatoxin A Induces Subconductance States in Ca2+ Release Channels (Ryanodine Receptors) of Cardiac and Skeletal Muscle . J Gen Physiol 1 May 1998; 111 (5): 679–690. doi: https://doi.org/10.1085/jgp.111.5.679
Download citation file:
Sign in
Don't already have an account? Register
Client Account
You could not be signed in. Please check your email address / username and password and try again.
Could not validate captcha. Please try again.
Sign in via your Institution
Sign in via your InstitutionSuggested Content
Unitary Ca2+ Current through Mammalian Cardiac and Amphibian Skeletal Muscle Ryanodine Receptor Channels under Near-physiological Ionic Conditions
J Gen Physiol (September,2003)
Ca2+ Sparks and Embers of Mammalian Muscle. Properties of the Sources
J Gen Physiol (June,2003)
Interdomain Interactions within Ryanodine Receptors Regulate Ca2+ Spark Frequency in Skeletal Muscle
J Gen Physiol (December,2001)
Email alerts
Advertisement