Stretch activated channels in proprioceptive organs of crab and crayfish are sensitive to gadolinium but not amiloride, ruthenium red or low pH

The type of stretch activated receptors (SARs) in the chordotonal organs in the crab walking leg and of the muscle receptor organ (MRO) in the crayfish abdomen have not yet been classified as to their molecular or pharmacological profile. The purpose of this study is to examine the pharmacological profile of SARs in the proprioceptive neurons in the crab and crayfish models. Since many SARs share the pharmacological profile of displaying low pH or being proton sensitive (i.e. being more active) or blocked by the diuretic amiloride or ruthenium red as well as being blocked by the broad stretch activated channel blocker gadolinium (Gd3+), we used these agents to screen the receptors. Various displacement rates as well as static positions that activate the stretch activated receptors were used in examining their pharmacological profiles. Hour-long exposure to low pH decreased neural activity of the chordotonal organ of the crab more so than to amiloride or ruthenium red. The crayfish MRO did not show pH sensitivity or sensitivity to amiloride or ruthenium red. Gd3+ rapidly blocked neural activity in both the crab and crayfish. It appears these stretch activated receptors may not have a classification that is suited to the standard pharmacological profiles. The molecular makeup of the channels also awaits characterization. This could reveal a novel SAR subtype. Our neurophysiology course1 took this project on as a course-based undergraduate research experience (CURE) to address an authentic research question.