Summer Research

* Student(s): Hannah Stahle , Angela Pagano , Sarah McNeil , Katie Lee
Advisor: David Gapp

Title: Regulation of smooth muscle contraction in the painted turtle


Hormonal and neural regulation of gastrointestinal smooth muscle contractility in reptiles has been poorly investigated. While the effects of some neurotransmitters such as acetylcholine, norepinephrine and serotonin have been documented in several species, little is known of other regulatory substances, especially hormonal and neural peptides. It was the purpose of this study to continue our ongoing investigation of Chrysemys smooth muscle contractility and a number of the factors regulating both contraction and relaxation.

Segments (2-3 cm) of upper and lower intestine from Chrysemys picta were excised and tied closed at both ends and placed in 30 ml water-jacketed muscle warmers containing aerated Locke's solution. Muscle warmers were maintained at 34-35 degrees Celsius using a circulating water bath. Each segment was attached to an F60 Myograph and contractile responses were recorded on a Narco Biosystems Physiograph MKIIIS.

Intestinal smooth muscle contracted predictably and consistently to carbachol over a range of 10^-7 to 10^-5M, an effect blocked completely by atropine. Hormonal peptides such as neurotensin and substance P also stimulated contraction and were independent of cholinergic mechanisms. Bradykinin was especially potent at inducing contraction and was also active in the presence of atropine. When testing for the minimal portion of the bradykinin molecule required for contraction, only bradykinin1-7 produced contraction while bradykinin1-5,, bradykinin1-6 and bradykinin 1-8 were without effect.

Relaxation effects of adrenergic compounds such as epinephrine, norepinephrine and isoproterenol were modest at best and often not inducible. These compounds, when added to contracting muscle, moderately reduced in total tension and duration of contractile activity induced by carbachol. Attempts at inducing relaxation by leu-enkephalin (10^-7 to 10^-5M) were unsuccessful.

In conclusion, contraction of Chrysemys intestinal smooth muscle appears to regulated by many of the same hormones and neurotransmitters employed by other vertebrates, however, there are some distinct differences that point to potentially unique properties of the turtle smooth muscle.

Summer stipend support provided by Bristol-Myers Squibb (AP, KL) and Merck/AAAS (HS, SM) grants.