In these studies we have examined rat kidneys biochemically and microscopic
ally to determine where myosin I beta is located before, during, and after
an acute ischemic injury. Myosin I beta is present in multiple tubule segme
nts including the brush border (BB) of the proximal tubule cell (PTC). Its
distribution is severely altered by a 15-min renal artery clamp. Myosin I b
eta is present in the urine during reflow and is found in the numerous cell
ular blebs arising from the damaged PTC and other tubules. Two hours of ref
low result in a decrease in BB myosin I beta staining and an increase in it
s cytoplasmic staining. Interestingly, the return of the F-actin in the BB
precedes the return of the myosin I beta, suggesting that this myosin I iso
form may not play a role in rebuilding the microvilli after an ischemic inj
ury. A nonstructural role for this myosin, such as transport or channel reg
ulation, is supported by its presence in many tubule segments, all of which
have transport and channel requirements but do not all contain microvilli.