  The effect of oxygen isotope substitution on Tc has been analyzed for heavily
underdoped and overdoped La2-xSrxCu1-yZnyO4 compounds with different Zn
contents in the CuO2 plane. The effect of Zn on the isotope exponent, {\alpha},
was more pronounced in the case of the underdoped (x = 0.09) compounds compared
to the overdoped (x = 0.22) ones. The variation of {\alpha} with in-plane
disorder can be described quite well within a model based solely on impurity
induced Cooper pair-breaking in the case of the underdoped compounds. This
model, on the other hand, fails to describe the behavior of {\alpha}(y) for the
overdoped samples, even though Zn still breaks pairs very effectively at this
hole (Sr) content. We discuss the implications of these finding in details by
considering the Zn induced magnetism, stripe correlations, and possible changes
in the superconducting order parameter as number of charge carriers in the CuO2
plane, p (\equiv x), is varied.
