Two functionally distinct forms of guanosine cyclic 3'-5'-phosphate stimulated cation channels in a bovine rod photorecptor disk preparation

Journal Article · Tue Jun 14 00:00:00 EDT 1988 · Biochemistry; (United States)

OSTI ID:6998244

Pearce, L B; Calhoon, R D; Burns, P R; Vincent, A; Goldin, S M

Cyclic nucleotide stimulated efflux of /sup 22/Na/sup +/ and /sup 45/Ca/sup 2 +/ from a purified bovine rod outer segment disk preparation was measured on the 25-100-ms time scale by a novel rapid superfusion method. Activation of cation efflux by 8-bromoguanosine cyclic 3',5'-phosphate (8-Br-cGMP) was maximal within 25 ms. Over a wide range of concentrations of 8-Br-cGMP, the kinetics of termination of efflux precisely conformed to the sum of two exponential decay processes: a rapid phase (decay constant of 200 ms) and a slower phase (decay constant of 1.6 s). The kinetics of the biphasic decay of efflux cannot be explained by depletion of a pool of releaseable /sup 22/Na but appear to reflect an intrinsic process of inactivation of the channels. 8-Br-cGMP stimulated release of actively accumulated /sup 45/Ca exhibited identical biphasic decay kinetics. The maximum rate of Ca release may be sufficient to produce a 1 ..mu..M change in local cytoplasmic (Ca) within 20 ms. The Ca:Na selectivity ratio is approx. 0.5:1 for both decay phases. 8-Br-cGMP demonstrated a lower potency but a higher degree of cooperativity in its activation of the rapid vs the slower decay phase of /sup 22/Na efflux. The slower phase of decay was selectively inhibited by 25 ..mu..M l-cis-diltiazem, a relatively weak inhibitor of the rapid decay phase. Sodium ion (5-10 mM) selectively inhibited the rapid decay phase of 8-Br-cGMP-stimulated /sup 45/Ca release. These two kinetically and pharmacologically distinct phases of decay are hypothesized to represent two functionally distinct forms of cGMP-stimulated cation channels.

• Research Organization: Harvard Medical School, Boston, MA (USA)
• OSTI ID: 6998244
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 27:12; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ALKALI METAL ISOTOPES
ALKALINE EARTH ISOTOPES
ANIMALS
AROMATICS
AZAARENES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BETA-PLUS DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
BIOCHEMISTRY
BODY
BODY AREAS
CALCIUM 45
CALCIUM ISOTOPES
CATTLE
CHEMISTRY
DAYS LIVING RADIOISOTOPES
DOMESTIC ANIMALS
EVEN-ODD NUCLEI
EYES
FACE
GUANOSINE
HEAD
HETEROCYCLIC COMPOUNDS
INTERMEDIATE MASS NUCLEI
ISOTOPES
KINETICS
LIGHT NUCLEI
MAMMALS
MEMBRANE TRANSPORT
NUCLEI
NUCLEOSIDES
NUCLEOTIDES
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANS
PIGMENTS
PROTEINS
PURINES
RADIOISOTOPES
REACTION KINETICS
RETINA
RHODOPSIN
RIBOSIDES
RUMINANTS
SENSE ORGANS
SODIUM 22
SODIUM ISOTOPES
VERTEBRATES
YEARS LIVING RADIOISOTOPES