Biomedical subjects

J I Choca

Publications and source records attributed to J I Choca.

4 recordsLinked to original sources

PubMed1988

A low-priced computer-assisted densitometer and analysis software for quantitative autoradiography.

A computer-assisted densitometer which consists of a darkroom enlarger, a black-and-white exposure meter, an amplifier, an analog-to-digital converter, and a microcomputer with a monitor and a graphic printer can be utilized for the quantitative analysis of autoradiograms. QUANTAR, a computer program written in BASIC, records the density measurements and stores the data in a file that can be easily retrieved by commercially available spreadsheet software. A spreadsheet template was designed to convert the digital readings into concentration of ligand in tissue. A variety of spreadsheet templates can be created to analyze data for a standard curve, a Scatchard plot, or a binding competition curve. This system, which is easy to assemble, may be useful to the frugal investigator with a modest equipment budget.

Adenosine↗

PubMed1988

Adenosine A1 and A2 receptors of the substantia gelatinosa are located predominantly on intrinsic neurons: an autoradiography study.

Tissue autoradiography was used to examine the distribution of A1 and A2 adenosine receptors in the rat spinal cord. The distribution of binding sites for the A1 selective agonist, N6-[3H]-[(R)-1-methyl-2-phenylethyl]adenosine (R-[3H]PIA), was similar to the distribution of binding sites for [3H]-5'-N-ethylcarboxamide adenosine [( 3H]NECA), an agonist that binds to A1 and A2 receptors with nearly equal affinities. Binding site densities were highest in the substantia gelatinosa, followed by lamina 10; the remainder of the spinal cord displayed uniformly low levels of binding sites. In each of these three areas, [3H]NECA bound to more sites than R-[3H]PIA. When the A1-selective agonist, N6-(cyclopentyl)adenosine, was used to block [3H]NECA binding to A1 receptors, the autoradiograms demonstrated a band of A2 receptor density which tended to be localized in the ventral portion of the substantia gelatinosa. Unilateral dorsal rhizotomy, hemitransection and complete transection of the spinal cord failed to alter the [3H]NECA or R-[3H]PIA binding in the substantia gelatinosa. In contrast, unilateral microinjections of kainic acid into the dorsal horn decreased [3H]NECA and R-[3H]PIA binding at the level of the injections by 42 and 37%, respectively. In some areas, kainic acid injection eliminated all R-[3H]PIA and [3H]NECA binding in the substantia gelatinosa. It is therefore concluded that spinal cord A1 and A2 adenosine receptors in the substantia gelatinosa are located predominantly on intrinsic neurons.

Adenosine↗

PubMed1987

Identification of A1 and A2 adenosine receptors in the rat spinal cord.

The adenosine receptors in membranes prepared from rat ventral and dorsal lumbar spinal cord were characterized by comparing the binding characteristics of [3H]5'-N-ethylcarboxamide adenosine ([3H]NECA), an agonist with nearly equal affinities at the A1 and A2 adenosine receptor subtypes, with those of [3H]N6-[(R)-1-methyl-2-phenylethyl]adenosine ([3H]R-PIA), an A1-selective agonist. Saturation isotherms of the ventral and dorsal spinal cord yielded Kd values 1.9 to 2.3 nM for [3H]R-PIA and 18.1 to 19.5 nM for [3H]NECA. The Bmax for [3H]NeCA was approximately twice the Bmax for [3H]R-PIA in ventral and dorsal halves (267 vs. 128 fmol/mg of protein and 402 vs. 206 fmol/mg of protein, respectively). Displacement of specific [3H]NECA binding by the A2-selective agonist, 2-(phenylamino)adenosine, the relatively nonselective antagonist, theophylline and six A1-selective agonists, R-PIA, S-PIA, N6-(cyclohexyl)adenosine, N6-(cyclopentyl)adenosine, N6-(m-aminophenyl)adenosine and N6-(m-iodophenyl)adenosine, revealed two [3H]NECA binding components with the characteristics of A1 and A2 receptors. All curves best fit a two-site model when analyzed by the computer program LIGAND. R-PIA, N6-(cyclohexyl)adenosine and N6-(cyclopentyl)adenosine were the most potent displacers at the first site (Ki = 0.6-1.4 nM). All A1-selective agonists were poor displacers of [3H]NECA at the second site (Ki = 0.6-18.6 microM). The A2-selective agonist, 2-(phenylamino)adenosine, was as potent as R-PIA in displacing [3H]NECA from this site with a Ki value 0.57 microM. Finally, the A1 and A2 adenosine receptor-mediated inhibition and stimulation of adenylate cyclase were demonstrated directly in synaptic membranes prepared from the spinal cord.

Adenosine↗

PubMed1985

Specific photoaffinity labelling of inhibitory adenosine receptors.

N6(L-phenylisopropyl)adenosine (L-PIA) and N6(3-iodo-4-azido benzyl)-adenosine (IAzBA) inhibit the adenylate cyclase activity in synaptic membranes of chick cerebellum via Ri adenosine receptors. [3H]L-PIA and [125I]AzBA bind to these membranes with Kd values of approximately 1 nM and Bmax values of approximately 1000 fmol/mg protein. Photolysis of [125I]AzBA bound to synaptic membranes results in the specific incorporation of radioactivity into a protein with Mr = 36,000. This photoincorporation is blocked by simultaneous exposure to L-PIA, theophylline, an adenosine receptor antagonist, or Gpp(NH)p, but not by cytosine, suggesting that the 36,000 dalton protein is the Ri adenosine receptor or a subunit of the receptor that contains the adenosine binding site.

Adenosine↗