Stretch-activated cation channels of leech neurons: characterization and role in neurite outgrowth

The goal of this study was to characterize the stretch-activated ion channe ls (SACs) of adult identified neurons of the leech Hirudo medicinalis and t o test the role of SACs in neurite outgrowth of isolated cells. Using cell- attached patch recording, we established that SACs are densely distributed in the growth cone membrane of cultured neurons. In excised patches, we fou nd that these channels are permeable to Ca2+, as well as to monovalent cati ons. The channels are blocked by the extracellular application of gadoliniu m (Gd3+), amiloride and gentamicin. Amiloride and gentamicin, respectively, induce a partial and complete voltage-dependent block. Time-lapse video re cordings of neurite outgrowth from single cultured neurons were used to stu dy the effects of blocking SACs with gentamicin. Within 20 h of plating in the presence of the aminoglycoside, the total length of neuronal arborizati on was significantly greater than that measured in its absence. The amount of assembled axon per unitary surface area remained constant over 40 h and did not differ significantly with or without gentamicin. Our findings show that SACs of leech neurons admit Ca2+, are densely distributed in the growt h cone membrane and exhibit typical pharmacological features of mechanotran sducer ion channels. In addition, our data suggest that these cation channe ls participate in the early interaction between growing neurites and cultur e substrate.