Biomedical subjects

A H Dittman

Publications and source records attributed to A H Dittman.

6 recordsLinked to original sources

PubMed1999

Functional identification of a goldfish odorant receptor.

The vertebrate olfactory system utilizes odorant receptors to receive and discriminate thousands of different chemical stimuli. An understanding of how these receptors encode information about an odorant's molecular structure requires a characterization of their ligand specificities. We employed an expression cloning strategy to identify a goldfish odorant receptor that is activated by amino acids-potent odorants for fish. Structure-activity analysis indicates that the receptor is preferentially tuned to recognize basic amino acids. The receptor is a member of a multigene family of G protein-coupled receptors, sharing sequence similarities with the calcium sensing, metabotropic glutamate, and V2R class of vomeronasal receptors. The ligand tuning properties of the goldfish amino acid odorant receptor provide information for unraveling the molecular mechanisms underlying olfactory coding.

Animals↗

PubMed1997

Sensitization of olfactory guanylyl cyclase to a specific imprinted odorant in coho salmon.

The role of cGMP in olfactory signaling is not fully understood, but it is believed to play a modulatory role in intracellular signaling in vertebrate olfactory receptor neurons (ORNs). Here, we present evidence that cGMP in ORNs may play an important role in recognition of biologically relevant odors and olfactory learning. Specifically, we investigated the cellular mechanisms underlying olfactory imprinting in salmon. Salmon learn odors associated with their natal site as juveniles and later use these odors to guide their homing migration. This imprinting is believed to involve sensitization of the peripheral olfactory system to specific homestream odorants. We imprinted juvenile salmon to the odorant beta-phenylethyl alcohol (PEA) and examined the sensitivity of olfactory adenylyl and guanylyl cyclases to PEA during development. Stimulation of guanylyl cyclase activity by PEA was significantly greater in olfactory cilia isolated from PEA-imprinted salmon compared with PEA-naive fish only at the time of the homing migration, 2 years after PEA exposure. These results suggest that sensitization of olfactory guanylyl cyclase may play an important role in olfactory imprinting by salmon.

Animals↗

PubMed1994

Evidence for a peripheral olfactory memory in imprinted salmon.

The remarkable homing ability of salmon relies on olfactory cues, but its cellular basis is unknown. To test the role of peripheral olfactory receptors in odorant memory retention, we imprinted coho salmon (Oncorhynchus kisutch) to micromolar concentrations of phenyl ethyl alcohol during parr-smolt transformation. The following year, we measured phenyl ethyl alcohol responses in the peripheral receptor cells using patch clamp. Cells from imprinted fish showed increased sensitivity to phenyl ethyl alcohol compared either to cells from naive fish or to sensitivity to another behaviorally important odorant (L-serine). Field experiments verified an increased behavioral preference for phenyl ethyl alcohol by imprinted salmon as adults. Thus, some component of the imprinted olfactory homestream memory appears to be retained peripherally.

Animals↗

PubMed1994

Oxidation of critical cysteine residues of type I adenylyl cyclase by o-iodosobenzoate or nitric oxide reversibly inhibits stimulation by calcium and calmodulin.

The calmodulin binding domain of the type I adenylyl cyclase has recently been identified as an amino acid sequence (residues 495-522) that contains 2 cysteine residues. Therefore, we examined the effect of several sulfhydryl reagents on the calmodulin sensitivity of the enzyme. Treatment of membranes containing the type I adenylyl cyclase with N-ethylmaleimide rapidly inhibited basal, calcium/calmodulin-stimulated, and forskolin-stimulated adenylyl cyclase activity. When the enzyme was treated with limiting amounts of o-iodosobenzoate, which oxidizes vicinal sulfhydryls to disulfides, stimulation by Ca2+ and calmodulin was eliminated at concentrations which did not affect basal adenylyl cyclase activity. Calmodulin stimulation of the enzyme was restored by treatment with dithiothreitol or glutathione which reduce disulfides to free thiols. NO and sodium nitroprusside also reversible inhibited calmodulin stimulation of the enzyme. We propose that the loss in calmodulin sensitivity caused by these reagents may be due to the oxidation one or more sets of vicinal thiols present in the enzyme.

Adenylyl Cyclase Inhibitors↗

PubMed1994

A novel mechanism for coupling of m4 muscarinic acetylcholine receptors to calmodulin-sensitive adenylyl cyclases: crossover from G protein-coupled inhibition to stimulation.

Muscarinic m4 acetylcholine receptors are normally coupled through Gi to inhibition of adenylyl cyclases. In the olfactory bulb and some cultured cells, however, m4 receptors can couple to stimulation of adenylyl cyclase activity. In this study, m4 receptors and specific isozymes of adenylyl cyclases were coexpressed in HEK-293 cells to characterize the mechanism(s) for m4 receptor stimulation of adenylyl cyclases. The calmodulin-sensitive type I and type III adenylyl cyclases were chosen for this study because neither enzyme is stimulated by the beta/gamma complex of G coupling proteins. M4 receptors exhibited either inhibition or stimulation of type I and III adenylyl cyclases depending upon receptor density and agonist concentration. Inhibition of adenylyl cyclase was apparently due to M4 coupling through Gi. Adenylyl cyclase stimulation through m4 receptors was not due to increases in intracellular Ca2+ and stimulation of the calmodulin-sensitive enzymes since it was evident in isolated membranes in the absence of free Ca2+ and with whole cells preloaded with the Ca2+ chelator BAPTA/AM. Stimulation of adenylyl cyclase activities by m4 receptors was apparently mediated via Gs since it was GTP-dependent, was insensitive to pertussis toxin, and was not due to beta/gamma stimulation. Synthetic peptides derived from a G protein activating region of the m4 receptor mimicked the m4-mediated stimulation of adenylyl cyclase activity. These data demonstrate a novel mechanism for muscarinic regulation of adenylyl cyclases that may involve crossover from inhibitory to stimulatory G protein coupling.

Adenylyl Cyclases↗

PubMed1993

Phorbol ester stimulation of the type I and type III adenylyl cyclases in whole cells.

Phorbol esters and activators of protein kinase C have been reported to either facilitate or inhibit increases in intracellular cAMP caused by activators of adenylyl cyclase. The variable responses to activators of protein kinase C may reflect, in part, the existence of distinct adenylyl cyclases present in animal cells. There are a family of adenylyl cyclases with different regulatory properties, and clones for six distinct types of adenylyl cyclase have been reported. Two of these enzymes, the type I and type III adenylyl cyclases, are stimulated by calcium and calmodulin whereas the others are not. In this study, we examined the effect of phorbol esters of the activity of the type I and type III adenylyl cyclases in whole cells. TPA markedly enhanced the forskolin responsiveness of the type I and type III adenylyl cyclases expressed in kidney 293 cells. The effect of TPA on the activity of the calmodulin-sensitive adenylyl cyclases was not mediated through increases in intracellular free calcium. These data suggest that activation of protein kinase C can elevate intracellular cAMP in animal cells that contain the type I or type III adenylyl cyclase.

1-Methyl-3-isobutylxanthine↗